UNIVERSITY  OF  CALIFORNIA 
LOS  ANGELES 


WORLD-LIFE 


COMPARATIVE  GEOLOGY. 


ALEXANDER   WINCHELL,  LL.D., 

PROFESSOR  OF  GEOLOGY  AND  PALEONTOLOGY  IN  THE  UNIVERSITY  or 
MICHIGAN. 


Geology  in  framing  its  conclusions  is  compelled  to  take  into  account  the 
teachings  of  other  sciences.— SIR  WILLIAM  THOMSON. 

La  geologic  suivie  sous  ce  point  de  vue  qui  la  rattache  a  1'Astronomie  pour- 
ra,  sur  beaucoup  d'objets,  en  acquerir  la  precision  et  la  certitude. — LAPLACE. 

Ewig  zerstort,  es  erzeugt  sich  ewig  die  drehende  Schopfung, 

Und  ein  stilles  Gesetz  lenkt  der  Verwandlungen  Spiel. — SCHILLER. 


CHICAGO: 
C.  GRIGGS   AND   COMPANY. 

1883. 


COPYRIGHT,  1883, 
BY  S.  C.  GRIGGS  AND  COMPANY. 


HIS  PUPILS  IN  THE  UNIVERSITY  OF  MICHIGAN, 

THIS    VOLUME    IS, 

WITH  PROPOUND  CONSIDERATION, 

AFFECTIONATELY    INSCRIBED 
BY 

THE  AUTHOR. 


PREFACE. 


rriHE  reader  will  find  in  the  following  pages  a  thoughtful  view  of 
r  the  processes  of  world  formation,  world  growth  and  world  deca- 
dence. I  have  gathered  together  here  many  of  the  important  facts 
observed  in  the  constitution  and  course  of  nature,  and  have  endeav- 
ored to  weave  them  into  a  system  by  the  connecting  threads  of  scien- 
tific inference.  I  have  aimed  to  incorporate  the  soundest  and  latest 
views  published  on  the  various  branches  of  the  subject;  and  have 
yet  felt  constrained,  in  so  wide  a  field,  and  so  unexplored  in  some  of 
its  nooks,  to  interpose  my  own  conclusions  in  some  cases  where, 
perhaps,  due  diffidence  should  have  restrained  my  pen.  Inevitably 
the  whole  discussion  is  conducted  from  the  standpoint  of  nebular 
cosmogony.  This,  as  will  be  seen,  has  shaped  the  views  presented 
on  the  accumulation  of  the  materials  for  world  formation,  on  the 
evolutions  of  nebulae,  stars  and  planets,  on  the  all-important  influ- 
ence of  tidal  action  in  cosmic  history,  and  on  the  grand  cycle  of 
cosmic  existence.  Appropriately  the  treatment  ends  with  a  histori- 
cal sketch  of  the  progress  of  opinion  toward  the  lofty  and  inspiring 
generalization  which  the  work  attempts  to  set  forth. 

The  motives  which  have  prompted  to  the  preparation  of  the 
work  are  four-fold . 

1.  I  felt  desirous  that  the  general  reader  should  be  able  to  find 
within  reach  some  simple,  yet  complete  and  connected,  account  of 
the  development  of  the  world  and  the  system  of  material  things  to 
which  we  belong.  Many  of  the  grandest  conceptions  of  modern 
science  fall  within  this  range.  Many  of  the  marked  advances  of 
modern  investigation  have  contributed  to  the  enlargement  of  our 
view  in  this  field.  Yet  there  is  no  work  in  the  English  language,  if, 
indeed,  in  any  language,  bringing  into  one  connected  course  of  dis- 
cussion all  the  questions  properly  incident  to  the  activities  of  world 


vi  PREFACE. 

life.  Different  persons  have  ably  investigated  different  branches 
of  the  general  theme,  as  the  reader  will  learn  in  the  sequel,  but 
no  one  has  brought  together  and  put  in  the  form  of  popular  state- 
ment the  chief  results  of  so  diversified-  a  range  of  researches. 
Many  thousands  of  intelligent  listeners  have  testified  their  appreci- 
ation of  the  expositions  offered  during  fifteen  years  past  from  the 
popular  platform;  but  these  expositions  have  been  necessarily  de- 
scriptive and  superficial,  while  many  questions  and  many  difficulties 
raised  by  the  hearer  had  to  be  left  unanswered.  Here  the  speaker 
sits  down  to  a  sober  talk  with  those  who  wish  to  listen  further.  I 
hope,  therefore,  the  present  work  will  find  a  welcome  among  the 
multitudes  who  have  caught  mere  glimpses  of  the  great  doctrine,  as 
well  as  the  large  class  of  readers  in  general  who  require  something 
more  substantial  than  our  popular,  fictitious  tales  of  society. 

2.  I  desired  to  offer  the  reader  a  portrayal  of  the  grand  system 
of  the  universe,  and  leave  him  with  a  profound  impression  of  the 
omnipresence  and  supremacy  of  One  Intelligence.     The  unity  and 
interdependence  of  all  parts  of  ihj  cosmic  mechanism,  from  nebula 
to  river  delta;  the  universality  of  nature's  forces,  and  the  uniform- 
ity of  nature's  modes  of  activity,  all  the  way  down  from  the  galaxy 
to  the  little  cascade  in  the  glen,  are  facts  of  such  stupendous  and 
impressive  significance  as  to  stir  the  imagination  and  arouse  the 
most  torpid  soul.     This  wonderful  concatenation  of  things  when 
once  glimpsed  by  the  timid  doubter,  must  force  a  conviction  of  the 
continuity  of  material  existence;  and  whoever  has  gained  that  con- 
viction, and  will  faithfully  question  his  own  consciousness,  will  soon 
be  convinced  that  that  which  is  interpreted,  and  can  only  be  inter- 
preted, in  terms  of  mechanism,  cannot  be  self-originated,  however 
remote  its  origin ;  nor  self-acting,  however  vast  its  extent  or  incom- 
prehensible its  activities. 

3.  I  desired  to  induct  the  earnest  student  of  nature,  young  or 
old,  into  MR-  vestibule  of  celestial  mechanics,  and  leave  him  with 
an  inspiration  which  should  carry  him   on  to  the  pursuit  of  the 
higher  methods  of  physical  investigation.      I  have  hoped,  also,  to 
-hnw  him  that  the  fields  of  truth  are  not  fenced  off  from  each  other 
and  limited  by  the  narrow  definitions  of  the  sciences.     The  fences 
are  all  down,  and  it  is  all  one  domain.     The  geologist  tries  to  work 


PREFACE.  vii 

out  the  constitution  and  life  history  of  our  planet.  For  the  study 
of  its  accessible  parts  he  needs  to  use  the  appliances  and  results 
of  the  whole  round  of  the  sciences.  To  its  interior  he  cannot  pene- 
trate; but  he  finds  the  planet  journeying  on  a  course  of  change 
which  leads  directly  from  a  state  of  high  primitive  incandescence; 
and,  lifting  his  eyes,  he  beholds  the  incandescent  state  as  a  common 
incident  in  the  vicissitudes  of  worlds.  He  cannot  transport  himself 
across  the  intervals  of  geologic  aeons,  but  he  can  gaze  upon  other 
worlds  just  entering  upon  states  passed  millions  of  years  ago  by  our 
earth;  or  states,  even,  which  will  be  reached  by  our  planet  some 
millions  of  years  in  the  future.  I  have  attempted  to  take  the  reader 
over  the  system  of  evidences  from  which  he  may  thus  reason  in 
laying  the  foundations  of  a  science  which,  from  one  point  of  view, 
may  be  styled  the  geology  of  the  stars;  and,  from  another,  the 
astronomy  of  the  earth.  It  is  the  science  of  Comparative  Geology. 
It  is  Astrogeology.  It  yields  to  no  science  in  the  fruitfulness  and 
fascination  of  its  conceptions. 

4.  It  has  been  a  part  of  my  purpose,  also,  to  clear  up  the  most 
serious  difficulties  encountered  by  belief  in  the  nebular  origin  of 
our  planetary  system.  At  the  present  day  the  objections  heard  do 
not  proceed  to  .any  considerable  extent  from  proper  representatives 
of  scientific  opinion,  but  from  intelligent  persons  who  fear  that  the 
interests  of  religious  faith  are  jeopardized  by  the  acceptance  of  any 
form  of  evolution.  Some  of  these  have  honored  me  by  very  special 
attentions.  They  have  challenged  me  to  controversy,  and  their 
abettors  have  sometimes  jeered  me  over  my  assumed  inability  to  rise 
from  the  pile  of  ruins  which  has  been  made  of  me  and  my  theoiy. 
I  need  not  disguise  the  satisfaction  which  I  feel  in  the  arrival  of  the 
convenient  time  when  these  gentle  gladiators  shall  discover  them- 
selves battering  their  blades  against  a  wall. 

While  the  fundamental  conception  underlying  the  course  of 
reasoning  here  pursued  is  that  of  nebular  evolution :  and  while  the 
general  method  of  the  evolution  conforms  to  the  celebrated  hypothe- 
sis of  Laplace,  it  would  be  an  error  to  conceive  the  present  work  an 
attempt  to  establish  the  "hypothesis  of  Laplace."  In  the  first 
place,  the  general  principles  of  nebular  cosmogony  were  the  growth 
of  a  century  and  a  half;  and  the  ideas  contributed  by  Kant  and  Sir 


viii  PREFACE. 

William  Herschel  were  certainly  not  less  guiding  and  determinative 
than  the  services  of  the  Marquis  de  Laplace.  In  the  next  place,  the 
development  of  the  doctrine  has  continued  ever  since  the  Systtine 
dn  Monde  was  published.  Since  the  invention  of  the  spectroscope, 
the  nebular  cosmogony  has  undergone  important  modifications.  A 
number  of  the  ablest  investigators  of  the  present  generation  have 
given  their  best  efforts  toward  putting  the  general  doctrine  in  a 
consistent  shape.  Nor  can  it  be  correctly  said  that  the  general  the- 
ory remains  still  in  the  status  of  a  hypothesis.  In  certain  points  of 
detail,  opinion  may  still  remain  divided;  but  when  a  hypothesis  has 
stood  the  scrutiny  of  three  generations,  and  has  become  all  but 
unanimously  accepted  by  those  prepared  to  form  original  opinions, 
as  the  real  expression  of  a  method  in  nature,  surely,  then,  the  time 
has  passed  when  any  person  can  advantageously  illustrate  his  learn- 
ing and  sagacity  by  continuing  to  reproach  the  conception  as  "a 
mere  hypothesis."  If  any  "  mere  hypothesis  "  ever  strengthened  into 
the  condition  of  a  scientific  doctrine,  assuredly  we  find  in  the  scien- 
tific world  to-day  the  general  features  ot  a  sound  nebular  doctrine. 

In  style  and  treatment  the  present  work  possesses  a  double  char- 
acter. The  general  reader  may  confine  himself  to  the  body  of  the 
discus-ion,  untcrrified  by  the  nature  of  the  foot  notes,  and  find  a 
simple,  continuous  treatment  of  the  theme  which,  I  hope,  will  sat- 
isfy his  expectations.  But  if  any  one  desires  to  know  by  what 
means  sonic  of  tlic  statements  of  the  text  have  been  established,  he 
will  find  frequently  in  the  foot  notes  the  indications  of  simple 
mutliematical  operations,  which  may  yield  him  some  additional 
gratification.  And  if  he  feel  prompted  to  pursue  still  further  any 
brunch  of  the  ini|uiry,  the  accompanying  references  to  the  literature 
of  the  subject  will  enable  him  to  follow  the  masters  of  science  into 
their  most  recondite  investigations.  Thus,  for  one  class,  the  book  is 
suited  to  be  read  rapidly  and  laid  aside;  for  another  class  it  is  a 
ti-M  l»>ok  which  may  be  studied. 

The  general  conception  of  world  life  here  set  forth  has  occupied 
the  author's  thoughts  for  many  years;  and  by  writing  and  by  popu- 
lar lectures,  us  well  as  before  university  classes,  he  has  endeavored 
to  ili-eminate  truthful  and  inspiring  estimates  of  the  method  of 
the  world's  growth.  He  lias  stood  for  the  defence  of  nebular  theory 


PREFACE.  ix 

when  it  had  few  friends,  and  when  its  enemies  were  prompted  as 
much  by  sentiment  as  by  good  reason.  The  great  idea  was  fascinat- 
ing; its  magnificence  took  possession  of  the  imagination,  and  its 
symmetry  and  coherence  commanded  rational  conviction.  It  now 
commands  the  admiration  and  championship  of  the  scientific  world. 

I  feel  that  it  is  entirely  improbable  that  all  errors  of  statement 
have  been  avoided  through  all  the  details  of  the  discussion.  The 
intelligent  reader  will  discover  many  points  where  I  have  had  to  cut 
loose  from  the  moorings  of  high  authority  and  venture  among  the 
breakers  of  independent  speculation.  It  is  only  justice  to  myself, 
also,  to  state  that  all  the  main  positions  of  the  work  were  taken 
and  reduced  to  writing  more  than  two  years  ago.  Many  of  those 
which  at  the  time  were  new,  or  seemed  to  be  new,  were  presented  in 
public  lectures  as  early  as  1878  and  1879.  Since  these  dates  many 
advances  in  observation  and  in  theory  have  been  made,  and  not  a 
few  along  those  very  lines  which  I  had  worked  out.  Since  my  first 
enunciations,  Xordenskjold,  Tissandier  and  the  British  Association 
have  done  much  to  establish  the  doctrine  of  disseminated  cosmical 
dust;  Sir.  W.  Siemens  has  published  his  speculations  on  the  sources 
of  the  sun's  heat;  M.  Faye  has  investigated  the  geology  of  the 
moon;  Mr.  (now  Professor)  G.  H.  Darwin  has  published  his  beauti- 
ful analytical  investigations  of  the  evolution  of  a  rotating  viscous 
spheroid;  and  Rev.  0.  Fisher  has  collected  in  a  handsome  volume 
his  researches  on  the  physics  of  the  earth's  crust.  If  there  remain 
any  thoughts  or  suggestions  which  may  fairly  be  ascribed  to  the 
author  of  this  work,  the  scientific  reader  will  find  it  out;  and  I  have 
only  to  hope  that  they  may  be  found  adequately  supported  by  evi- 
dence ;  and,  finally,  that  the  whole  discussion  may  afford  the  reader 
a  degree  of  pleasure  equal  to  that  experienced  by  the  writer  in 
bringing  the  discussion  to  its  present  shape. 

University  of  Michigan,  September,  1883. 


OOXTESTTS. 


PART  I. 

WORLD    STUFF. 
CHAPTER   I. 

COSMICAL    DUST. 

jj  1.    METEORS. 

1.  Phenomena  and  Physical  Characters     ....  3 

2.  Meteoroidal  Orbits 17 

§  2.  ZODIACAL  LIGHT 23 

§  3.  COMETS 27 

1.  Phenomena  and  Constitution        .         .         .         _        .27 

2.  Connection  of  Comets  and  Meteors   ....  33 

£  4.  SATURNIAN  RINGS 35 

^  5.  XEBUL^E .35 

1.  Their  Existence 35 

2.  The  Spectroscope  and  Its  Applications       ...  37 

3.  Forms  of  Nebula? 42 

£  6.  UNIVERSAL  WORLD  STUFF 48 

1.  Theory  of  Cosmical  Dust 48 

2.  Theory  of  Elemental  Atoms 49 

(1.)  History  of  Opinions 49 

(2.)  Siemens'  Hypothesis  Concerning  Solar  Heat       .  56 

§  7.  A  COSMICAL  SPECULATION 65 

1.  Aggregation  of  Cosmical  Matter        ....  65 

2.  Cosmical  Matter  as  a  Resisting  Medium          .         .         .70 

3.  Genesis  of  Nebula?  and  Comets           ....  71 

4.  Vicissitudes  of  Comets  within  Our  System     .  .74 

xi 


CONTENTS. 


CHAPTER  II. 

NEBULAR    LIFE. 

j<  1.  NEBULAR  HEAT 81 

1.  Heat  Produced  by  Refrigerative  Contraction      .         .  81 

2.  Changes  in  the  Forms  of  Nebulae                                       -  87 

3.  Heat  Arising  from  the  Aggregative  Process       .         .  92 
§  2.  NEBULAR  ROTATION 94 

1.  Causes  of  Rotation 94 

2.  Causes  of  Nebular  Forms     .-•...     99 

3.  Influence  of  Resisting  Medium  .         .         .         .104 

4.  Nebular  Evolution  without  Rotation     ....    105 
§  3.  NEBULAR  ANNULATION 106 

1.  The  Law  of  Equal  Areas 10G 

2.  Abandonment  of  a  Ring 110 

3.  Determination  of  the  Width  of  the  Ring       .        .         -  111 

4.  Non-Annulating  Nebulae  and  Stratified  Rings    .         .        118 
§4.  SPHERATION  OF  RINGS 119 

1.  Disruption  of  a  Ring        -        -        .         .        .         .119 

2.  Rotation  of  Resulting  Mass 121 

3.  Influence  of  Cosmic  Tides 129 

4.  Ultimate  Synchronism  of  Axial  and  Orbital  Motions      .  134 

5.  Summary  of  Laws  of  Rotation          ....       134 

6.  Arrangement  of  Heavier  Matters  on  the  Derived  Sphe- 

roid   137 

7.  Orders  of  Nebuhe     .  139 


CONTENTS.  Xlll 

PART    II. 

PLAXETOLOGY. 

CHAPTER  I. 

ORIGIN    OF    THE    SOLAR    SYSTEM. 

§  1.  VERIFICATION  OF  NEBULAR  THEORY  FROM  FACTS         .        .  147 

1.  Phenomena  of  the  Solar  System        ....       147 

A.  Demonstrative  Phenomena    .....  147 

B.  Phenomena  Apparently  Confirmatory         .         .       149 

2.  Phenomena  External  to  the  Solar  System       .         .         .150 
§  2.  OBJECTION'S  BASED  ON  RELATIONS  OF  PLANETARY  MOTIONS      158 

1.  Retrograde  Motions 153 

(1.)  Caused  by  Perturbative  Attractions  .         .  154 

(2.)  Caused  by  Coalescence  of  Planetary  Constituents  .  157 
(3.)  Caused  by  a  Certain  Relation  of  Rotary  Motion  of 

the  Nebula          .  157 

(4.)  M.  Faye's  Explanation     .....  158 

2.  The  Periodic  Times  Too  Long 158 

(1.)  Effect  of  Subsequent  Planetauon       .         .         .159 
(2.)  Effect  of  Great  Central  Condensation  of  the  Annu- 

lating  Spheroid 161 

3.  The  Periodic  Times  Too  Short 167 

4.  The  Periodic  Time  of  Phobos  Too  Short        .         .        .  168 

5.  No  Adequate  Cause  for  Rotary  Motion       .         .         .170 
§  3.  OBJECTIONS  BASED  ON  RELATIONS  OF  PLANETARY  POSITIONS  171 

1.  Orbital  Inclinations 171 

2.  Interplanetary  Intervals 173 

3.  Elliptic  Forms  of  Orbits  .         .         .         ...       173 

(1.)  Effect  of  Subsequent  Planetation          .         .         .174 
(2.)  Effect  of  Perturbative  Influences      ...       175 
§  4.  OBJECTIONS  BASED  ON  RELATIONS  OF  PLANETARY   MASSES 
AND  DENSITIES  .        -  175 


xiv  CONTENTS. 

1.  The  Aggregate  Asteroidal  Mass  Too  Small         .         .       175 

2.  Disrupted  State  of  the  Asteroidal  Mass          .         .        .176 

(1.)  Contingencies  of  a  Stratified  Ring    .        .         .176 
(2.)  Possible  Fate  of  an  Intra-Jovian  Ring  .         .  177 

(3.)  Effect  of  Excessive  Undulations  in  a  Fluid  Ring  177 

3.  Low  Densities  of  the  Exterior  Planets  .        .        .         -  177 
§  5.  OBJECTION  BASED  ON  RELATION  TO  TERRESTRIAL  DURATION  179 
§  6.  OBJECTIONS  BASED  ox  RELATIONS  OF  COMETS,  STARS  AND 

NEBULAE  ..........  181 

1.  The  Comets  Irreconcilable  with  the  Theory        .         .        181 

(1.)  Neither  Laplace  nor  Other  Astronomers  have  In- 
cluded Comets  in  Our  System's  Nebular  History  .  182 

(2.)  Some  Comets  must  Approximate  Planetary  Condi- 
tions  183 

(3.)  The  Physical  Relations  of  Comets  to  Our  System  are 
Acquired  ........  183 

2.  Matter  of  Requisite  Tenuity  could  Not  Exist     .         .       184 

3.  The  Separation  of  a  Ring  Improbable  .        .         .         .186 

(1.)  Reason  and  Observation  Affirm  the  Possibility  .       186 
(2.)  M.  Faye's  Objections  Considered  .        .         .         .187 

4.  The  Diverse  Constitution  of  the  Fixed  Stars      .         .       191 

(1.)  No  Universal  Homogeneity  of  Matter  Assumed     .  191 
(2.)  Stellar  Spectra  Testify  the  Opposite  of  the  Claim  191 
6.  Nebular  Spectra  Indicate  Too  Low  a  Pressure        .         .  192 
(1.)  Nebular  Theory  is  Not  Staked  on  Spectra  of  Neb- 

»!«• 192 

(2.)  The  Spectra  do  Testify  a  Self-luminous,  Tenuous 

Vapor 192 

(3.)  Adverse  Spectral  Evidence  Outweighed  .  .  193 
S  7.  WHAT  THE  NEBULAR  THEORY  DOES  NOT  IMPLY  .  .  .196 
§  8.  PROPOSED  MODIFIED  FORMS  OF  NEBULAR  THEORY  .  .  198 

1.  M.  Faye's  Proposed  Modification 198 

Critical  Remarks  on  M.  Faye's  Theory     .  208 

2.  Spiller's  Proposed  Modification     .  .  212 


CONTENTS. 


CHAPTER  II. 

GENERAL  COSMOGONIC  CONDITIONS  ON  A  COOKING   PLANET. 

§  1.  RELATIVE  AGES  OF  PLANETS  IN  A  SYSTEM  .        .        .        .215 

§  2.  PASSAGE  TO  THE  MOLTEN  PHASE 217 

§  3.  SUPERFICIAL  SOLIDIFICATION  PROM  COOLING  .  .  .  218 
§  4.  INTERNAL  SOLIDIFICATION  FROM  PRESSURE  .  .  .220 
g  5.  MAXIMUM  INTERNAL  TEMPERATURE  ON  AN  INCRUSTED  PLANET  221 
§  6.  TIDAL  ACTION  AND  ITS  CONSEQUENCES  ....  222 

1.  Some  Elementary  Principles      .         _  .       _         .         .       222 

2.  General  Effects  of  Tidal  Action  in  Planetary  Life          .  230 

(1.)  Rotational  Retardation  Caused  by  Lagging  Tide  232 
(2.)  Recession  of  Tide-Producer  Resulting  from  Same  239 
(3.)  Inez-eased  Inclination  of  Axis  of  Tide-Bearer  Re- 
sulting from  Same        ._....  243 

3.  Tendency  to  Synchronism  of  Rotary  and  Orbital  Motions  248 

4.  Predetermination  of  Submeridional  Trends  ...  252 

5.  Outflow  of  Molten  Matter 255 

6.  Crushing  Effects  of  Tidal  Deformation          .         .         .  255 

7.  Marine  Tides  in  the  Early  History  of  a  Planet   .         .       256 

§  7.  LIQUEFACTION  OF  WATER 270 

§  8.  TRANSFORMATIONS  OF  THE  PLANETARY  CRUST  .        .        .274 
§  9.  PLANETOGRAPHIC   EFFECTS   OF   CERTAIN  CHANGED  ASTRO- 
NOMICAL CONDITIONS          .  278 

1.  Changes  in  Velocity  of  Rotation        ....       278 

2.  Retarded  Orbital  Motion 281 

3.  Increase  of  Obliquity  of  Axis  to  Plane  of  Orbit         .       282 

4.  Change  in  Relative  Positions  of  Apsides  and  Equinoxes  .  285 

5.  Changes  of  Orbital  Eccentricity        ....       288 
§  10.  OROGENIC  FORCES 291 

1.  Theory  of  Upheaval  by  Aeriform  Agents  .         .         .       292 

2.  Theory  of  a  Molten  Nucleus  and  a  Wrinkling  Crust       .  294 

3.  Theory  of  Copious   Sedimentation  along  Geosynclinals  314 


xvi  CONTENTS. 

4.  Theory  of  Mashing  Together 319 

5.  Statement  of  Separate  Constructive  Conceptions  Rela- 

tive to  Mountain  Making 323 

6.  Final  Conception  of  Orogenic  History        ...  326 

7.  Analytical  Conspectus  of  Orogenic  Speculations     .         -  831 
§  11.  UNEQUAL  THICKNESS  OF  PLANETARY  CRUST  .        .         .  333 

CHAPTER  III. 

SPECIAL    PLANETOLOGY;    OR,    PRESENT    CONDITION    AND 
COSMOGONIC  HISTORY  OF  THE  PLANETARY  BODIES  OF 

OUR    SYSTEM. 

§  1.  THE  EARTH .        -        -  338 

1.  Condition  of  the  Earth's  Interior      .        .        .        .339 

(1.)  Fluidity  of  a  Certain  Zone 344 

(2.)  Fluidity  Resulting  from  Relief  of  Pressure        .      345 
(3.)  Tidal  Deformation  and  Volcanic  Phenomena         .  346 

2.  Submeridional  Trends  in  the  Earth's  Primitive  Structure  350 

3.  The  Earth's  Age,  with  Methods  of  Estimation       .         .  355 

(1.)  Time  Required  for  Contraction  of  the  Sun         .        355 
(2.)  Time  Required  for  Cooling  of  the  Sun  .         .  356 

(3.)  Time  Required  for  Cooling  of  the  Earth   .        .       356 
(4.)  Time  Required  for  Deposition  of  All  the  Rocky 

Sediments 356 

(5.)  Method  Based  on  Disturbance  from  Continental 

Elevation .        .366 

(6.)  Calculation  Based  on  Secular  Variation  of  Eccen- 
tricity          368 

(7.)  Estimates  Based  on  Rates  of  Erosion  and  Deposition  369 
(8.)  The  Rate  of  Terrace  Formation  .         .         .         .374 
(9.)  Under-rate  of  Increase  of  Internal  Heat  beneath 
Regions  Anciently  Covered  by  an  Ice  Cap     .         .  376 

§  2.  TUB  MOON 379 

1.  Planctological  Retrospect 379 


CONTENTS.  XV11 

2.  Tidal  Forces  on  the  Moon 383 

3.  Physical  Aspects  of  the  Moon 385 

4.  Tidal  Evolution  of  the  Moon 395 

5.  The  Atmospheric  Factor  in  Lunar  History    .         .         .  410 
§  3.  MARS 415 

1.  Phenomena  of  Mars,  and  Their  Interpretation       .         .  415 

2.  Tidal  and  Atmospheric  Influences  on  Mars         .         .       417 
§  4.  THE  INFERIOR  PLANETS 420 

1.  Venus 420 

2.  Mercury 423 

§5.  JUPITER 425 

1.  Physical  Relations 425 

2.  Jupiter's  Retarded  Development        ....       429 

3.  Tidal  Action  on  Jupiter 434 

4.  Tidal  Effects  and  Densities  on  Jupiter's  Satellites       .       438 
§  6.  THE  ULTRA-JOVIAN  PLANETS 442 

CHAPTER  IV. 

PLANETARY     DECAY;     OR,     COSMIC     CONDITIONS     MORE 
ADVANCED    THAN    THE    TERRESTRIAL    STAGE. 

§  1.  EXTREMELY  ERODED  CONDITIONS 451 

§  2.  PROGRESSIVE  SUBSIDENCE  OF  TEMPERATURE    ...       458 

1.  Shrinkage  and  Acceleration  of  Axial  Motion          .         .  459 

2.  Absorption  of  Water  and  Atmosphere       .         .         .460 

(1.)  Index  of  Rock  Absorption  by  Volume  .         .         .460 
(2.)  The  Volume  of  the  Ocean        .         ...       466 
(3.)  Calculation  of  Absorptive  Capacity  of  the  Planet- 
ary Pores 467 

§  3.  SYNCHRONISTIC  MOTIONS  AND  TIDAL  FINALITIES  .  .  473 
§  4.  INFLUENCE  OF  INTERPLANETARY  MATTER  .  .  .  .477 
§  5.  GENERAL  REFRIGERATION  ..-.-.  484 

1.  Planetary  Refrigeration 484 

2.  Solar  Refrigeration 484 


xviii  CONTENTS. 

(1.)  Inductive  Evidences  of  Lowered  Terrestrial  Tem- 
perature     ........  485 

(a)  In  Historic  Times 485 

(6)  In  Prehistoric  Times       .        .        .        '        .485 

(c)  Cause  of  Secular  Deterioration  of  Climates   .       486 

(2.)  Deductive  Considerations  Touching  Secular  Cooling  489 

3.  Revivification  of  a  Dead  Universe         ....  491 

CHAPTER  V. 

HABITABILITY    OF    OTHER    WORLDS. 

§  1.  SOME  REFERENCES  TO  LITERATURE  ON  THE  SUBJECT  .  .  496 
§  2.  THE  HUMAN  STANDARD  OF  HABITABILITY  NOT  ABSOLUTE  .  497 
§  3.  HABITABILITY  UNDER  THE  HUMAN  STANDARD  .  .  .500 

PART  III. 

GENERAL    COSMOGONY. 
CHAPTER  I. 

FIXED    STARS    AND    NEBULAE. 

§  1.  CONDITIONS  OF  THE  FIXED  STARS 511 

1.  Double,  Triple  and  Multiple  Stars     .        .         .         .511 

2.  Temporary  Stars 513 

3.  Variable  Stars 518 

4.  Gradations  of  Stars 522 

5.  Indications  of  Incipient  Stellation     ....       530 
§  2.  COSMOOONIC  CONDITIONS  OK  NEBULA          .        .        .        .531 

CHAPTER  II. 

THE    COSMIC    CYCLE. 

§  1.  THE  KEYS  OF  COMPARATIVE  GEOLOGY  .  .  .  .534 
§  2.  THE  FINAL  GENERALIZATION 538 

1.  Stages  of  World  Life  .......  538 

2.  Some  Final  Deductions    .        .  544 


CONTENTS.  XIX 

PART  IV. 

EVOLUTION    OF    COSMOGONIC    DOCTRINE. 
CHAPTER  I. 

PRE-KANTIAN    SPECULATIONS. 

§  1.  GREEK  PHILOSOPHERS 551 

§  2.  SPECULATIONS  OF  KEPLER      ......       553 

§  3.  THE  VORTICAL  THEORY  OF  DESCARTES        ....  554 

§  4.  THE  THEORY  OF  LEIBNITZ 558 

1.  His  Protogaea .558 

2.  His  Planetogeny 564 

§  5.  THE  VORTICAL  THEORY  OF  SWEDENBORG     ....  566 
§  6.  THE  SPECULATIONS  OF  THOMAS  WRIGHT          .        .        .572 

CHAPTER  II. 

KANT'S  GENERAL  HISTORY  OF  NATURE. 

§  1.  FlRMAMENTAL  ORGANIZATION .574 

§  2.  PLANETOGENY      ....__._       577 

§  3.  THE  COSMOS  IN  ITS  TOTALITY 583 

§  4.  OUR  SUN  AND  OTHER  SUNS 587 

§  5.  THE  MECHANICAL  CONSTITUTION  OF  THE  WORLD          .        .  589 
§  6.  DEDUCTIONS  TOUCHING  HABITABILITY  AND  UNITY  IN  THE  591 

SYSTEM  OF  WORLDS 593 

§  7.  SYNOPSIS  OF  POINTS  IN  THE  COSMOGONIC  THEORY  OF  KANT 

1.  Points  Considered  Well  Taken 593 

2.  Points  Considered  Incorrectly  Taken          .  595 

CHAPTER  III. 

DR.    LAMBERT    AND    SIR    WILLIAM    HERSCHEL. 

§  1.  LAMBERT'S  COSMOLOGICAL  LETTERS   .....  597 


XX  CONTENTS. 

§  2.  SIR  WILLIAM  HERSCHEL'S  RESEARCHES  ....       598 

1.  The  Structure  of  the  Heavens       .        .        .  .528 

2.  Nebular  Studies        .  601 

CHAPTER  IV. 

LAPLACE'S  SYSTEM  OP  THE  WORLD.  » 

§  1.  PRELIMINARY  VIEWS  ON  NEBULAE  AND  GENERAL  PHYSICAL 

ASTRONOMY      .        -        .    - GOG 

§2.  HYPOTHESIS  TOUCHING  THE  GENESIS  OF  THE  SOLAR  SYSTEM  Gil 

1.  Former  Expansion  of  the  Solar  Atmosphere  .        .         .612 

2.  Formation  and  Abandonment  of  Zones  of  Vapor       .       613 

3.  Rupture  and  Planetation  of  Rings        _  614 

4.  Relations  of  Comets  and  Zodiacal  Light    ...       615 

5.  Lunar  Synchronistic  Motions        .....  615 

CHAPTER  V. 

SYSTEMATIC    RESUME    OF    OPINIONS. 


LIST  OF  ILLUSTRATIONS. 


1.  Corpuscles  of  Magnetic  Iron  from  the  Snow  on  Mont  Blanc 

at  the  Altitude  of  2,710  Metres  XoOO        .         .         .         .10 
From  Tissandier. 

2.  Corpuscles  of  Magnetic  Iron  Collected  from  Rain  Water  at 

Sainte  Marie  du  Mont  X500 10 

From  Tissandier. 

3.  Corpuscles  of  Magnetic  Iron  from  the  Dust  Collected  in  the 

Unfrequented  Towers  of  Notre  Dame  de  Paris  .          .     10 

From  Tissandier. 

4.  Fall  of  a  Bolide  at  Queengouck,  India          .         _        _         .12 

From  a  Drawing  by  Lieutenant  Aylesbury. 

5.  The  Positions  of  the  August  and  November  Meteoroidal 

Swarms  .          ........     19 

Compiled  by  the  Author. 

6.  The  Great  Nebula  in  Orion.     Central  Part  .  .42 

From  a  Drawing  by  Trouvelot. 

7.  Sickle-shaped  Nebula.     Herschel  3,289  -     43 

After  Schellen. 

8.  Spiral  Nebula  in  Canes  Venatici.     Herschel  1,622         .        .    44 

After  Schellen. 

9.  Spiro-annular  Nebula.  Herschel  604  ....    44 

After  Schellen. 

10.  Spiro-annular  Nebula.     Herschel  854.     Indications  of  Sev- 
eral Rings 45 

After  Schellen. 

11.  Annular  Nebula  in  the  Lyre 46 

From  a  Drawing  by  Professor  Holden. 

12.  Planetary  Nebula,  without  a  Nucleus.    Herschel  2,241       .       46 

After  Schellen. 

13.  Planetary  Nebula  with  two  Nuclei.     Herschel  838      .         .    47 

After  Schellen. 
14  Ideal  Illustration  of  the  Streams  of  Outflowing  and  Inflowing 

Matter  on  the  Sun 60 

After  Siemens. 

xsi 


xxii  LIST   OF   ILLUSTRATIONS. 

15.  Motion  of  a  Body  in  the  Presence  of  Two  Other  Bodies         .     67 

Original. 
10.  The  Omega  Nebula  in  Sagittarius      .         .        .         .        .89 

From  a  Drawing  by  Lasell  in  1862. 

17.  The  Omega  Nebula 90 

From  a  Drawing  by  Trouvelot  and  Holden  in  1875. 

18.  The  Trifid  Nebula         " 91 

From  a  Drawing  by  Trouvelot. 

19.  Motion  of  Three  Nebulae  in  Space,  Case  I,  Sub-case  I  .     95 

Original. 

20.  Motion  of  Three  Nebulas  in  Space,  Case  I,  Sub-case  II          .     96 

Original. 

•21.  Motion  of  Three  Nebulae  in  Space,  Case  II          ...     97 
Original. 

22.  Rotation  Resulting  without  Actual  Impact         .        .        .98 

Original. 

23.  Possible  Origin  of  the  Falcate  Form  of  Nebula         .         .  103 

Original. 

24.  Coagulating  Nebula,  or  "Curdling  Fire  mist"          .         .  105 

Original. 

25.  Formation  of  Local  Nuclei  in  a  Nebula  .          .         .  106 

Original. 

26.  The  " Law  of  Equal  Areas"      .        .         .        .  .     ..        .108 

Original. 

27.  Nebula  in  Process  of  Annulation 113 

Original. 

28.  Illustrating  the  Determination  of  the  Width  of  a  Nebulous 
Ring 114 

Original. 

29.  Nebula  Becoming  Annular        .         .         .  .        .   117 

Original. 

30.  Stratification  of  a  Nebulous  Ring 119 

Original. 

31.  Nebulous  Ring  Undergoing  Rupture          .        .        .        .120 

Original. 

32.  Sphcration  of  a  Nebulous  Ring          ...  .120 

Original. 

33.  Prolateness  and  Rotation  of  the  Derived  Spheroid       .         .  130 

Original. 

34.  Inversion  of  the  Orbit  of  a  Satellite  .         .        .        .155 

Original. 


LIST   OF    ILLUSTRATIONS.  xxiii 

35.  Process  of  Lengthening  the  Periodic  Time  and  Acquiring 

an  Elliptic  Orbit 160 

Original. 

36.  Increase   of  Density  toward   the   Centre  of  the  Nebulous 
Spheroid  .          .  164 

Original. 

37.  Deforraative  Tide 226 

Original. 

38.  Compound  Tide 226 

Original. 

39.  Film  Tide 227 

Original. 

40.  Quantitative  Relations  of  Tides 228 

Original. 

41.  Illustrating  a  Lagging  Tide       .         .         .        .         .         .232 

Original. 

42.  Illustrating  the  Secular  Effects  of  Tides  in  a  Rotating  Vis- 
cous Spheroid 236 

Original. 

43.  Discordant  Tides  of  a  Nucleus  and  Film  .         .         .239 

Original. 

44.  Varying  Reaction  Resulting  from  Varying  Viscosity  .  242 

Original. 

45.  Tidal  Increase  and  Diminution  of  Obliquity        ...  245 

Original. 

46.  The  Tide-Bearer  Viewed  as  Tide-Producer          .         .         .246 

Original. 

47.  Ascent  of  Isothermal  Planes  in  a  Planet's  Crust          .         .  276 

Original. 

48.  Climatic  Effect  of  Increased  Obliquity  of  a  Planetary  Axis     283 

Original. 

49.  Climatic  Effect  of  Change  in  Relative  Positions  of  Apsides 
and  Solstices 287 

Original. 

50.  Illustrating  the  Formation  of  Mountain  Wrinkles        .         .  299 

After  M.  Alphonse  Favre. 

51.  Formation  of  Wrinkles  in  a  Planetary  Crust,  with  Parallel 
Contiguous  Furrows         .-._...  300 

Original. 

52.  Section  through  the  Alps,  Showing  the  Effects  of  Lateral 
Pressure 310 

After  Heim. 


xxiv  LIST   OF   ILLUSTEATIONS. 

53.  Diagram  of  Niagara  Gorge,  Old  and  Xew  .        .        .370 

After  Belt. 

54.  Map  of  the  Moon 366 

After  M.  Faye. 

55.  Section  across  the  Crater  Copernicus  ....  387 

After  M.  Faye. 

5G.  Map  of  the  Crater  Theophilus,  and  Surrounding  Region       .  388 
After  Neison. 

57.  Action  of  an  Internal  Tide  against  the  Crust      .        .        .398 

Original. 

58.  Effect  of  Discordant  Lagging  Tides  .         .        .        .398 

Original. 

59.  The  Disappearance  of  the  Land  .        .        .  455 

Original. 


PART  I. 
WORLD-STUFF. 


Ante,  mare  et  tellus,  et,  quod  tegit  omnia,  ccelum, 

Unus  erat  toto  Naturae  vultus  in  orbe, 

Quern  dixere  Chaos ;  rudis  indigestaque  moles ; 

Nee  quidquam,  nisi  pondus  iners;  congestaque  eodem 

Non  bene  juuctarum  discordia  semina  rerum. — OVID. 


WORLD-LIFE. 


CHAPTEE  I. 
COSMICAL  DUST. 

I  know  no  recent  observation  in  physical  geography  more  calculated  to 
impress  deeply  the  imagination  than  the  testimony  of  this  presumably  meteoric 
iron  from  the  most  distant  abysses  of  the  ocean.  To  be  told  that  mud  gather}; 
on  the  floor  of  these  abysses  at  an  extremely  slow  rate  conveys  but  a  vague 
notion  of  the  tardiness  of  the  process.  But  to  learn  that  it  gathers  so  slowly 
that  the  very  star-dust  which  falls  from  outer  space  forms  an  appreciable  part 
of  it,  brings  home  to  us,  as  hardly  anything  else  could  do,  the  idea  of  undis- 
turbed and  excessively  slow  accumulation.— ARCHIBALD  GEIKIE. 

§  1.     METEORS. 

TTTHEXCE  comes  the  "Dust  of  Time?"  There  is 
VV  nothing  around  which  the  dust  of  time  does  not 
gather.  It  accumulates  among  the  shelters  of  the  moun- 
tain cliffs.  It  falls  upon  ivy-mantled  towers  and  ruined 
walls,  and  creates  a  rooting  place  for  many  a  hardy  herb, 
and  a  nidus  for  countless  living  germs.  It  clogs  the 
water-passages  from  our  roofs,  and  fills  our  cisterns  with 
soils  yielded  by  the  atmosphere.  It  gathers  about  de- 
serted structures;  it  buries  the  foundations  of  columns 
and  temples;  and  new  temples  are  built  upon  founda- 
tions which  have  older  foundations  beneath  them.  The 
ancient  cities  of  the  East  and  of  the  West  lie  slumbering 
beneath  the  accumulations  of  this  dust.  Nineveh  is  rec- 
ognized only  as  a  mound  of  earth.  Troy  lies  almost  be- 
neath the  reach  of  Schliemann's  spade.  The  cities  of 
3 


4  COSMICAL   DUST. 

Cyprus,  the  Morea,  and  the  Roman  Peninsula  are  but 
slowly  undergoing  fresh  exposure  to  the  light  of  day. 

Whence  the  dust  which  has  buried  walls  and  towers 
and  cities  ?  Let  us  answer  the  question  with  soberness. 
The  crumbling  of  wooden  beams,  and  even  of  the  solid 
stones,  has  supplied  the  larger  portion  of  the  debris  which 
mantle  the  foundations  of  the  ancient  cities.  Much  of  the 
soil  which  gathers  upon  roofs  and  in  the  crevices  of  old 
walls  has  been  lifted  by  the  winds  from  bare  field  and 
dusty  street.  Even  the  snowy  summits  of  the  Alps  *  be- 
come stained  by  terrestrial  particles  borne  by  upward  cur- 
rents into  the  mountain  air.  And  yet  I  will  venture  the 
opinion  that  some  dust  comes  to  the  earth  daily  which 
had  never  belonged  to  the  earth  before.  Out  from  the 
depths  of  space  —  beyond  the  clouds  —  beyond  the  atmos- 
phere—  from  a  granary  of  material  germs  which  stock  the 
empire  of  the  blue  sky,  comes  a  perpetual  but  invisible 
rain  of  material  atoms  —  like  the  evening  dew,  emerging 
from  the  transparency  of  space  into  a  state  of  growing 
visibility.! 

This  is  a  somewhat  unfamiliar  thought.  I  will  endeavor 
to  indicate  the  steps  of  evidence  by  which  it  is  reached. 

First,  the  METEORS  yield  both  suggestion  and  proof. 
That  mysterious  visitant  which  paints  its  luminous  streak 
along  the  evening  sky — sudden,  brilliant,  but  evanescent 
—what  is  it  ?  And  what  does  it  signify?  Mankind  for 
ages  have  gazed  upon  it  with  contemplative  awe.  Ac- 
cording to  most  recent  scientific  opinion,  it  is  a  mass 
of  matter  from  outer  space,  which  has  become  entangled 
in  the  exterior  limits  of  our  atmosphere,  and,  impeded 
in  its  movements  by  atmospheric  resistance,  has  been 

*  M.  Tissandier  reports  magnetic  particles  of  iron  dust  at  a  height  of  0,000 
n  the  slopes  of  Mont  Blanc,  and  other  elevated  positions. 
It  has  heen  quite  a  surprise  to  the  author  to  find  a  similar  conception 
thrown  out  by  an  anonymous  writer  several  years  since  (North  American  Re- 
vtew,  xcix,  28,  note,  July,  1864.) 


METEORS.  5 

overcome  by  the  attraction  of  the  earth,  and  deflected 
into  a  new  path.  It  now  moves  obliquelv  toward  the 
earth.  The  condensation  of  the  air  in  front,  caused  by 
its  rapid  movement,  develops  an  intense  heat.  The  cold 
meteor  is  lighted  up;  it  glows  for  an  instant,  but  the  heat 
becomes  so  intense  that  its  entire  mass  sometimes  is  con- 
verted into  vapor  and  strewn  along  the  sky,  to  shine  as 
a  luminous  streak  after  the  bolide  has  ceased  to  pursue  its 
course.  The  train  of  incandescent  vapor  retains  its  lumi- 
nosity, at  times,  for  one,  two  or  five  minutes,  floating  like 
a  cobweb  in  the  atmosphere,*  and  as  it  cools  it  fades  from 

*  During  the  meteoric  shower  of  November  14,  1868,  Professor  Maria  Mitch- 
ell noted  a  train  which  lasted  forty-four  minutes,  and  underwent  remarkable 
distortions  of  form.  (See  American  Journal  of  Science,  II,  xlvii,  400.)  The 
game  was  seen  by  Professor  J.  R.  Eastman  at  Washington,  to  last  thirty  min- 
utes (Report,  November  23,  18ti8).  The  phenomenon  has  been  discussed  by 
Professor  H.  A.  Newton  (American  Journal  of  Science,  II,  xlvii,  40St.  Changes 
of  form  and  position  of  meteoric  trains  have  been  mentioned  by  Sir  John  Her- 
schel  and  others.  Professor  E.  E.  Barnard,  for  instance,  of  Nashville,  Tennes- 
see,  writes  to  Nature  (xxv,  173,  December  23,  1881)  that  a  meteoric  train  re- 
mained visible,  November  16,  to  the  naked  eye,  six  minutes,  and  with  telescopic 
aid,  fifteen  minutes,  and  floated  meantime,  four  degrees.  On  the  contrary,  Ad- 
miral Krusenstern  states  that  he  saw,  during  his  voyage  around  the  world,  the 
train  of  a  fire-ball  shine  for  an  hour  after  the  luminous  body  itself  had  disap- 
peared, and  scarcely  move  throughout  the  whole  time  (Krusenstern :  Reise,  Th.  i, 
S.  58). 

If  the  visibility  of  the  train  results  from  incandescence,  it  is  difficult  to  un- 
derstand how  it  remains  so  long  in  an  assemblage  of  particles  fine  and  buoyant 
enough  to  float  in  the  upper  atmosphere.  Is  it  an  electric  or  a  phosphorescent 
glow?  Humboldt  in  a  note  (Cosmos,  Ott.;  trans.  Harper  ed.,  i,  142)  says  "sev- 
eral physical  facts  appear  to  indicate  that  in  a  mechanical  separation  of  matter 
into  its  smallest  particles,  if  the  mass  be  very  small  in  relation  to  the  surface, 
the  electrical  tension  may  increase  sufficiently  for  the  production  of  light  and 
heat."  Thus,  while  we  are  forced  to  admit  the  first  flash  of  a  meteoric  streak 
as  implying  actual  incandescence,  it  seems  not  improbable  that  the  fainter  and 
prolonged  glow  is  electric.  In  this  connection  I  am  reminded  to  cite  a  pas- 
sage from  Professor  Joseph  Lovering:  "Finally,  I  may  notice  the  light  enjoyed 
in  cloudy  nights  which  cannot,  Arago  supposes,  come  from  the  stars,  but  from 
the  phospho.-escent  clouds.  It  is  never  so  dark  out  of  doors  as  in  a  subterranean 
apartment,  or  in  a  room  without  windows.  During  the  dry  mist  of  1783,  the 
sky  was  as  bright  as  during  the  full  moon  when  overclouded.  Is  this  light  the 
glow-discharge  of  electricity?  If  so,  has  the  solar  light  the  same  electrical  origin 
more  intensely  developed?  And  is  the  colored  light  which  Nicholson  saw  in 
the  clouds  on  the  30th  of  July,  1797,  the  result  of  processes  similar  to  those 
that,  give  a  color  to  certain  of  the  stars  which  differ  from  the  white  sun-light?  " 
(Loveriug.  Patent  Office  Report,  1855,  Agriculture^  356.) 


6  COSMIC  A  L   DUST. 

view.  But  let  us  not  lose  sight  of  the  matter  which  un- 
derwent ignition;  it  is  not  annihilated  ;  it  has  not  been 
returned  to  the  regions  beyond  our  atmosphere;  those  are 
physical  impossibilities.  Unseen,  unheard,  millions  of 
particles  of  cooled  vapor  remain  floating  in  our  air.  Be- 
ing ponderable,  being  mineral  and  mostly  metallic,  they 
must  settle  toward  the  earth.  They  are  plunged  into  the 
vortices  of  the  winds;  they  are  soaked  up  by  aqueous 
vapors;  they  are  floated  by  clouds,  they  are  washed  down 
by  rivers  and  added  to  the  volume  of  the  globe.* 

That  this  conclusion  is  well  founded  we  have  abundant 
evidence.  Every  one  understands  that  the  atmosphere  is 
freighted  with  minute  solid  particles.  These  were  elabo- 
rately investigated  by  Ehrenberg  thirty  or  forty  years  ago, 
who,  like  Pasteur  and  Tyndall  in  more  recent  researches, 
directed  attention  more  especially  to  organic  substances, 
particularly  minute  germs  and  bacterial  organisms.  Few 
people  understand  that  the  atmosphere  bears  also  a  large 
proportion  of  mineral  substances,  some  of  which  must, 
almost  to  a  certainty,  have  an  extra-terrestrial  origin.  A 
careful  compilation  of  facts  has  been  made  by  M.  Gaston 
Tissandier  in  his  work  on  atmospheric  dust.f 

As  to  atmospheric  dust  of  terrestrial  origin,  investiga- 
tion shows  that  the  larger  part  is  taken  up  by  winds  from 
the  deserts  of  Sahara  and  Gobi.  The  African  dust  has 
descended  in  scores  of  recorded  showers  in  all  parts  of 
Europe,  as  well  as  in  the  Atlantic  ocean  along  a  belt  of 
1,500  miles,  and  as  far  as  300  miles  from  land.  The  Mon- 
golian dust  falls  chiefly  in  northern  China,  and  is  con- 
ceived by  Baron  von  Richthofen  to  be  the  source  of  a  vast 

*  The  foregoing  obvious  inferences  were  penned  and  made  part  of  a  lecture 
in  1877.  Since  that  date  the  writer  has  discovered  a  large  amount  of  evidence 
bearing  on  the  question  of  cosmical  dnst,  as  the  statements  and  references  in 
the  next  following  paragraphs  will  show. 

t Tissandier:  Leu  ponimieret  de  fair,  Paris,  1877.  See  also  Popular  Science 
Monthly,  xvii,  344-50,  July,  1880. 


METEORS.  7 

geological  deposit  known  as  loess.  The  volcanoes  of  Java, 
Central  America  and  Iceland  have  also  emitted  astonish- 
ing volumes  of  dust  which  was  floated  hundreds  of  miles. 
Amongst  organic  substances  found  in  nearly  all  parts  of 
the  world  sometimes  occur  enormous  quantities  of  pollen 
cells  from  forests  of  coniferous  vegetation.*  The  particles 
of  smoke  arising  from  western  forest  and  prairie  fires  are 
often  wafted  from  Michigan  and  Wisconsin  to  Montreal 
and  New  York.  There  is  no  doubt  that  the  characteristic 
smokiness  of  the  atmosphere  during  the  mild  period  in 
November  following  the  occurrence  of  the  first  killing 
frosts,  and  known  in  America  as  the  Indian  Summer, 
is  simply  the  smoke  arising  from  the  autumnal  burnings 
of  the  recently  killed  and  wall  dried  vegetation  of  thinly 
settled  districts.  It  may  hence  be  inferred  that  this  feature 
of  the  Indian  Summer  will  grow  less  characteristic  as  set- 
tlement more  completely  clears  and  cultivates  the  surface. 
'But  atmospheric  dust  of  terrestrial  origin  has  no  bear- 
ing on  our  search  for  world-stuff.  Among  the  earliest  to 
suggest  a  cosmic  origin  for  certain  forms  of  atmospheric 
dust  were  Ehrenberg  and  Arago.  The  latter  in  his  Popu- 
lar Astronomy  f  says  it  may  be  presumed  that  showers  of 
dust  do  not  differ  materially  from  ordinary  meteoric  show- 
ers. The  dust,  he  says,  appears  to  contain  the  same  sub- 
stances as  meteoric  stones.  Ehrenberg  states  that  one 
element  in  the  colored  snows  examined  by  him  was  iron, 
and  he  expresses  the  hope  that  scientific  men  would  accu- 

*The  writer  recalls  an  occasion  in  1853  when  in  Alabama,  on  the  morning 
after  ;t  shower,  a  yellow  and  sulphur-like  deposit  was  left  wherever  the  water 
had  been  accumulated.  Investigation  showed  the  substance  to  consist  of  pol- 
len grains:  and  as  the  cypress  swamps  and  pine  forests  of  the  Gulf  region  were 
then  in  flower,  the  explanation  was  obvious.  Similar  "sulphur  showers''  have 
been  since  reported  as  far  north  as  the  Ohio  river,  and  also  in  the  countries  of 
southern  Europe.  A  case  is  recently  reported  in  Iowa  by  C.  E.  Bessey.  Amer. 
Naturalist,  xvii,  658,  June,  18S3. 

t  Arago:  Astronomle  Populaire,  t.  iv,  208.  See  also  CEuvres  completes  de 
Francois  Arago,  t.  xii,  293,  463,  etc. 


8  COSMICAL   DUST. 

mulate  the  substance  in  quantity,  and  compare  it  in  this 
state  with  fragments  of  aerolites,  and  inspect  microscopi- 
cally the  smallest  globules.  Baron  Reichenbach  in  1864* 
insisted  on  the  probability  that  meteorites  exist  in  the 
form  of  granules  and  dust,  that  they  descend  to  the  earth 
and  add  something  to  its  quantity  of  matter.  He  also  was 
apparently  the  first  to  detect  nickel  and  cobalt  in  atmos- 
pheric dust,  and  these  furnish  the  critical  demonstration 
of  its  meteoric  origin.  M.  Daubr6e,  in  his  celebrated 
memoir  on  meteorites,!  speaking  of  the  meteorite  of  Or- 
gueil,  says  it  is  ''very  instructive  in  reference  to  the  exist- 
ence of  meteoric  dust,"  and  proceeds  to  explain  how  the 
disintegration  of  such  a  body  would  supply  it.  Among 
the  first  to  produce  evidence  in  support  of  the  theory  of 
the  cosmic  origin  of  certain  portions  of  the  atmospheric 
dust  was  Baron  A.  E.  Nordenskj5ld4  He  reported  large 
patches  of  arctic  ice  covered  with  a  gray  diatomaceous 
powder  mingled  with  grains  of  magnetic  iron  surrounded 
by  iron-oxide,  and  containing  also  probably  carbon.  Simi- 
lar deposits  were  reported  from  snows  from  the  neighbor- 
hood of  Stockholm,  from  the  interior  of  Finland  and  from 
Spitzbergen.  He  reports  the  detection  of  nickel  and 
cobalt  in  dust  from  the  middle  of  Greenland,  and  states 
that  he  is  personally  convinced  that  certain  hail  from  near 
Stockholm  was  formed  around  particles  of  cosmic  origin 
floating  in  the  air  and  falling  continually  to  the  earth. 
He  also  indicates  the  presence  of  a  brown  carbonaceous 
material  like  that  afforded  by  the  meteoric  iron  from 
Ovifak,  which  is  characterized  by  a  very  disagreeable 
odor  and  seems  to  be  oryanic.  Baron  Nordenskjold  has 

*  Reichenbach,  Poggendorff's  Annalen,  cxxiii,  368-74, 1864 ;  Cosmos,  29  Dec. 
1864. 

t  Daubrtfe,  Journal  des  Savons,  1870. 

$  See  a  note  by  M.  Daubree  In  Comptes  Rendus,  Ixxvii,  464,  18  Aug.  1873, 
and  Ixxviii,  236,  26  Jan.  1874.  Also  Poggendorff's  Annalen,  cl,  154,  1874,  and 
Am.  Jour.  Sci.,  Ill,  ix,  145-6. 


METEORS.  9 

more  recently  reported  further  observations.*  He  states 
that  the  snow  of  the  coast  of  the  Taimur  peninsula  was  cov- 
ered with  yellow  specks  of  carbonate  of  lime  of  an  unusual 
form  of  crystallization,  and  these  he  believed  to  be  of 
interplanetary  origin.  The  carbonate  of  lirne  found  by 
others,  as  well  as  all  organic  traces,  has  generally  been 
referred  to  a  terrestrial  origin;  but  this,  after  all,  may  be 
an  error. 

At  the  meteorological  station  of  Yeneseisk,  Marx  col- 
lected a  quantity  of  brick-red  dust  which  was  brought 
down  from  the  atmosphere  during  a  gale,  accompanied  by 
snow  and  rain,  October  31,  1881.  An  examination  of 
this  by  Professor  Lenz  shows  it  to  consist  of  iron,  nickel 
and  cobalt  ;  and  he  entertains  no  doubt  of  its  cosmical 
origin,  pointing  out  the  fact  that  it  was  observed  on  a  day 
very  near  to  the  appearance  of  the  November  meteors,  f 

M.  Tissandier  has  made  quite  extensive  researches  on 
atmospheric  dust,  and  has  put  beyond  question  the  mete- 
oric origin  of  certain  portions  of  it.  Many  grains  and 
minute  globules  of  iron  are  met  with  in  these  dust-falls, 
which  appear  to  have  been  fused  ;  and  it  is  shown  that 
in  certain  cases,  nickel  and  cobalt  are  present  in  the  iron, 
precisely  as  in  siderolites.  But  in  other  cases  these  sub- 
stances are  wanting,  and  these  are  cases  where  other  indi- 
cations point  to  a  tcrrestial  origin.  These  grains  of  mag- 
netic iron  have  been  collected  from  a  great  variety  of 
situations  —  from  the  summit  of  Mont  Blanc,  from  rains 
recently  fallen,  from  the  towers  of  Notre  Dame  cathedral 
in  Paris  and  many  other  cathedrals,  from  the  borders  of 
Lake  Lehman,  from  the  hospice  of  St.  Bernard  and  from 
many  localities  in  distant  countries.  Everywhere  are 

*NordenskjGld:  Tlie  Voyage  of  the  Vega  round  Asia  and  Europe.  Trans- 
lated by  Alexander  Leslie,  2  vols,  London,  1881. 

+  Lenz  in  Izvestla  of  the  Russian  Geographical  Society,  1883,  cited  in  Nature, 
xxvii,  4->2,  March  1,  1883. 


10  COSMICAL    DUST. 

found  these  iron  globules  bearing  the  unmistakable  marks 
of  fusion.  The  following  figures  are  copied  from  M.  Tis- 
sandier's  work  : 


**    *    * 


FIG.  1.  CORPUSCLES   OF  MAGNETIC  IRON,  PROM   THE  SNOW  OF  MONT  BLANC 
AT  THE  HEIGHT  OF  2,710  METRES.     X  500. 


Fio.  3.  CORPUSCLES  OF  MAGNETIC  IRON  COLLECTED  FROM  RAIN  WATER  AT 
SAINTE  MARIE  nu  MONT,     x  500. 


Fio.  3.    CORPUS<  LEW  OK  MAGNETIC  IRON  FROM  THE  DUST  COLLECTED  IN  THE 

I'NFHF.QUENTKl)   TOWERS   OF   NOTRE   DAME   DE    PARIS.      X  500. 

Most  of  the  writers  who  recognize  the  meteoric  origin 
of  these  grains  conceive  them  as  minute  meteorites,  while 
to  me  they  seem  rather  to  be  the  cooled  particles  of  the 
volatilized  bolide.  When  of  small  size,  the  bolide  is  com- 
pletely consumed,  when  too  large  for  a  destructive  heat  to 
penetrate  to  its  centre  during  the  brief  interval  of  the 
body's  descent  through  the  atmosphere,  it  is  only  the  surface 
which  undergoes  fusion,  and  this  is  swept  off  by  the  vio- 
lent impact  of  the  air,  and  broken  into  countless  minute 
particles.  Hence  the  exterior  of  a  fragment  of  meteoric 
iron  presents  those  peculiar  rounded  bosses  and  concavi- 
ties developed  on  the  surface  of  melting  ice. 


METEORS.  11 

Occasionally  these  bolides  attain  to  terrific  dimensions. 
The  accompanying  illustration,  also  from  Tissandier,  repre- 
sents the  bolide  which  preceded  the  fall  of  meteorites  at 
Queengouck,  India,  on  the  27th  of  December,  1857.  The 
train  shows  the  particles  of  molten  mineral  brushed  off  by 
the  impact  of  the  air.  The  drawing  was  executed  by 
Lieutenant  Aylesbury,  an  eye-witness  of  the  phenomenon, 
and  was  first  reproduced  by  Haidinger  in  his  Etude  sur  la 
chute  Queengouck. 

If  Mr.  John  Aitken's  theory  is  correct,  that  the  presence 
of  solid  particles  is  the  condition  of  vapor-condensation, 
then  the  highest  clouds  of  our  atmosphere  reveal  the 
presence  of  a  fine  dust,  and  this  very  probably  is  of  a  cos- 
mic character.* 

A  committee  of  the  British  Association  appointed  to  in- 
vestigate this  subject,  reported  through  Professor  Schuster 
in  188'3,f  that  rounded  particles  of  iron  containing  nickel 
and  cobalt  have  been  found  in  many  situations,  and  we  are 
constrained  to  ascribe  them  to  a  cosmic  origin. £ 

Thus  the  evidence  of  the  perpetual  arrival  of  foreign 
matter  from  the  interplanetary  spaces  seems  conclusive. 

*  See  Nature,  xxiii,  195-7,  December  30,  1880. 

t  See  abstract  in  Nature,  xxvii,  4S8. 

£  The  reader  will  find  a  summary  of  the  principal  cases  in  the  work  of  Tis- 
Biindier.  The  following  are  some  notices  of  more  recent  date.  Tacchini  re- 
ported iron  in  atmospheric  dust,  supposed  to  be  from  the  Sahara  (Academie  des 
Sciences,  28  June,  1880).  Professor  Sylvestri  of  the  Catania  Observatory,  re- 
ported a  dust-fall  with  much  metallic  iron  in  Sicily,  March  29-30,  1880  (Atti  del 
R.  Acudtima  del  Lincei,  fasc.  6,  May,  1880;  Nature,  xxi,  574,  xxii,  257).  On 
Sicilian  dust-falls,  which  have  been  particularly  frequent,  see  Lancetta  in  his 
Synthesis  of  meteorological  observations  in  Modica  and  Syracuse,  on  the  fall  of 
meteoric  powders  from  the  end  of  1876  to  April  16,  1880  (Rerista  Scientiflca- 
ludustriale,  No.  15,  August  1880).  M.  Danbree  reports  further  dust-falls  at 
Autun,  April  15,  1880,  and  in  the  Departments  of  the  Basses-Alpes,  Isere  and 
Ain,  France,  April  21-25,  1880  (Comptes  Rendus,  10  May,  1880),  as  also  in  Algiers, 
April  24-2(5,  1880  '(Nature,  xxii,  76).  Mr.  Murray  of  the  Challenger  found 
meteoric  dust  in  the  dredgings  from  the  bottom  of  the  sea.  (See  Archi- 
bald (Jcikic:  Geological  Sketches,  ch.  vi,  Humboldt  Library,  No.  39,  p.  35.)  Pro- 
fessor D.  Kirkwood  has  reported  a  dust-fall  in  Indiana,  March  28,  1880  (Popu- 
lar Science  Monthly,  xvii,  553). 


12 


COSMICAL   DUST. 


METEORS.  13 

An  insignificant  addition  to  the  earth's  mass,  the  reader 
may  think.  But  let  us  examine.  Ehrenberg  states  that  the 
mass  of  dust  which  fell  at  Lyons  in  1846,  over  an  extent  of 
400  square  miles,  was  estimated  by  the  French  savans  to 
be  7,200  quintals,  or  793  tons.  Chladni  calculated  that 
the  aerolites  enumerated  by  him  as  falling  between  1790 
and  1818  weighed  600  quintals,  and  on  this  basis  it  has 
been  held  that  the  daily  fall  of  atmospheric  dust  must  be 
millions  of  quintals.  Ehrenberg  calculated  that  243  quin- 
tals, or  27  tons,  of  red  dust  fell  with  snow  over  100  square 
miles  in  the  mountains  about  Salzbourg,  on  the  6th  of 
February,  1862.  According  to  M.  Calvert,  15  French  tons 
per  square  mile  fell  in  Carniola  on  the  5th  of  April,  1869. 
Baron  Nordenskjold  says  :  "  I  estimate  the  quantity  of 
the  dust  that  was  found  on  the  ice  north  of  Spitzber- 
gen,  at  0.1  to  1  milligram  per  square  metre,  and  probably 
the  whole  fall  of  dust  for  the  year  exceeded  the  latter  fig- 
ure. But  a  milligram  (.0188  grain)  on  every  square  metre 
of  the  earth  amounts  for  the  whole  globe  to  five  hundred 
million  kilograms  (say  half  a  million  tons)." 

Some  of  these  estimates  embrace,  undoubtedly,  dust 
transported  from  the  Sahara.  Let  us  then  direct  attention 
to  unquestioned  meteoric  matter.  It  is  said  on  good 
authority,  that  seven  and  one-half  millions  of  meteors 
bright  enough  to  be  seen  by  the  naked  eye,  pass  through 
our  atmosphere,  on  an  average,  every  twenty-four  hours, 
"and  this  number  must  be  increased  to  four  hundred 
millions  if  those  be  included  which  a  telescope  would 
reveal."*  On  special  occasions  they  are  seen  to  fall  like 

*Schellen:  Spectral  Analysis,  Am.  ed.  404.  Mr.  Denning  (Observatory, 
April  1883)  states  as  a  result  of  a  rough  computation,  that  about  two  hundred 
and  sixty  telescopic  meteors  appear  hourly  in  a  space  fifty  degrees  square 
(using  a  ten-inch  reflector  and  comet  eye-piece),  while  the  number  of  naked- 
eye  meteors  on  the  same  space  averages  only  twelve ;  so  that  the  proportion  of 
telescopic  and  naked  eye  meteors  is  as  twenty-two  to  one.  If  then  we  assume 
seven  and  one-half  millions  as  the  number  of  naked-eye  meteors  in  the  whole 


14  COSMICAL    DUST. 

drops  of  rain  in  a  brisk  shower.  Arago  estimated  that  he 
saw  two  hundred  and  forty  thousand  in  three  hours,  from 
his  place  of  observation,  on  the  12th  of  November,  1833. 
My  father,  who  witnessed  this  remarkable  shower,  has 
often  described  the  spectacle  which  he  beheld  before  day- 
light on  that  memorable  morning,  in  such  terms  that  it  is 
easy  to  believe  that  hundreds  of  millions  passed  before  his 
eyes  within  a  space  of  one  or  two  hours.  The  sky  was 
woven  into  a  network  of  fiery  fibres,  and  the  snow  on  the 
ground  glowed  with  a  red  illumination.  Suppose  each 
meteor  to  contain  but  ten  grains  of  matter,  if  four  hun- 
dred millions  enter  our  atmosphere  every  twenty-four 
hours,  this  is  two  hundred  and  eighty-six  tons  daily,  or 
one  hundred  and  four  thousand  three  hundred  and  fifty- 
two  tons  every  year.  In  one  hundred  million  years  this 
amounts  to  ten  million  four  hundred  and  thirty-five  thou- 
sand two  hundred  millions  of  tons.*  Now,  while  a  few 
grains  of  matter  in  a  state  of  intense  incandescence  may 
emit  sufficient  light  to  be  visible  at  a  distance  of  twenty 
to  fifty  miles,  it  is  not  probable  that  the  average  bolide  of 
observation  has  a  mass  as  low  as  ten  grains.  Thousands 
of  them  possess  too  great  a  mass  to  be  vaporized  in  the 
brief  time  spent  in  passing  through  the  atmosphere;  and 
then  they  reach  the  earth  as  meteorites,  and  constitute 
meteoric  stones,  aerolites  and  siderolites  or  meteoric  iron. 
In  this  condition  they  have  been  found  weighing  several 
pounds,  and  occasionally  several  tons.  In  January,  1879, 
a  meteoric  body  struck  a  house  in  Indiana,  and  in  its 

sky  in  twenty-four  hours,  there  should  be  one  hundred  and  sixty-live  million 
telescopic  meteors  in  the  same  time.  Mr.  Denning1  s  estimates,  however,  are 
far  below  the  figures  given  by  Schellen  and  here  used. 

*  Nevertheless  this  would  produce  a  film  only  one-twelve  hundred  and  fif- 
tieth of  an  inch  thick  over  the  whole  earth.  M.  Dufour  (Comptes  Itendus,  Ixii, 
840)  has  raised  the  (jiiestmn  whether  the  addition  of  meteoric  matter  to  the 
earth  may  not  be  the  cause  of  the  secular  acceleration  of  the  moon;  but  he  has 
evidently  exasperated  the  imi>ortance  of  these  additions.  This  acceleration 
moreover  is  otherwise  explained. 


METEORS.  15 

descent  to  the  cellar,  passed  through  the  body  of  a 
mau  in  bed.*  The  intense  and  unequal  heating  of  the 
exterior  and  interior  portions  of  the  larger  meteorites  is 
probably  the  cause  of  those  occasional  explosions  which 
scatter  brilliant  fragments  over  areas  miles  in  width,  and 
send  the  report  of  a  detonation  to  human  ears.  Many 
meteoric  masses  when  found,  present  a  surface  smoothed 
and  wrought  into  conchoidal  depressions,  and  presenting, 
in  many  respects,  the  appearance  of  a  mass  of  rapidly 
melting  ice.  Sometimes  many  distinct  furrows  have  been 
sunken  in  the  surface,  showing  the  channels  along  which 
the  liquefied  portions  have  been  driven  off  behind,  as  the 
body  shot  through  the  air. 

Chemical  analysis  shows  that  meteorites  are  composed 
of  well  known  terrestrial  substances.  The  most  abundant 
element  is  iron,  but,  in  union  with  this,  nickel  always 
occurs,  and  sometimes,  also  cobalt,  copper,  tin  and 
chromium.  Other  elements  are  silicon,  oxygen,  hydrogen, 
sulphur,  phosphorus,  carbon,  aluminium,  magnesium,  cal- 
cium, sodium,  potassium,  manganese,  titanium,  lead, 
lithium  and  strontium.  The  silicon  generally  appears  as 
silicates  of  various  bases.  Among  the  silicates,  olivine  is 
noteworthy  as  a  greenish  glassy  mineral  common  in  vol- 
canic rocks.  Augite  is  another  silicious  mineral  of  similar 
terrestrial  associations. 

Meteorites  have  been  observed  at  calculated  altitudes 
of  forty-six  to  ninety-two  miles.  They  move  with  veloci- 
ties ranging  from  fourteen  miles  to  one  hundred  and 
seven  miles  a  second.  If  we  suppose  a  dark  mass  of 
matter  moving  at  the  rate  of  twenty-seven  miles  a  second, 
to  meet  the  earth,  itself  moving  nineteen  miles  a  second, 
and  consider  that  the  earth's  attraction  would  develop  an 

*This,  according  to  the  Indianapolis  Journal,  was  Mr.  Lconidas  Grovcr 
;'who  resided  in  the  vicinity  of  Newtown,  Fountain  county,  near  Covington, 
Indiana." 


16  COSMICAL  DUST. 

additional  velocity  of  six  miles  a  second,  we  have  an 
aggregate  velocity  of  fifty-two  miles  a  second.  With 
such  a  velocity,  some  of  these  meteorites  plunge  into  our 
atmosphere.  It  hence  becomes  intelligible  that  even  in 
the  most  rarefied  portions  of  the  atmosphere,  the  conden- 
sation in  front  of  a  meteorite  moving  with  such  velocity 
must  develop  sufficient  heat  to  result  in  incandescence, 
and  even  in  volatilization.  Sir  William  Thomson  deter- 
mined by  experiment  that  a  body  moving  through  the  air 
at  the  rate  of  one  hundred  and  twenty-five  feet  per  second, 
develops  one  degree  of  heat,  and  that  with  increased 
velocities,  the  increase  of  heat  is  proportional  to  the  square 
of  the  velocity.  From  this  principle  it  is  easy  to  calculate 
that  a  velocity  of  four  thousand  feet  per  second  would 
cause  a  heat  of  over  one  thousand  degrees,  and  a  velocity 
of  forty-four  miles  per  second  would  give  a  temperature 
of  three  or  four  million  degrees.  Long  before  any  such 
temperature  is  actually  reached,  the  substance  of  the 
meteoroid  is  dissipated  in  vapor. 

At  the  beginning  of  this  century,  it  was  generally  be- 
lieved that  aerolites  were  either  condensations  of  vapors 
arising  from  the  earth,  or  were  projected  from  lunar  vol- 
canoes. It  has  indeed  been  argued  by  Chladni,*  by 
Halley,f  and  by  Lichtenstein,J  that  aerolites  are  of  cosmic 
origin;  but  this  point  was  not  clearly  established  until 
1833,  when  Professor  Olmstead  showed  that  the  November 
meteorites  of  that  year  all  radiated  from  one  point  in  the 
constellation  Leo,  and  could  not,  therefore,  have  partaken 
of  the  rotary  motion  of  the  earth.  This  conclusion  was 
eagerly  accepted  by  Poisson.  Arago  was  the  first  to  sug- 
gest §  the  periodicity  of  meteoric  showers;  but  it  required 

*  Chladni :  Ueber  den  Ursprung  der  von  Pallas  gefundenen  und  anderen 
Eitenmaseen. 

t  Halley,  Phil.  Trans.,  xxix,  161-3. 

J  Lichtenstein,  Gdttingen  Tatchenbuch. 

S  Arago,  Annuaire,  1836,  p.  297. 


METEORS.  17 

a  third  of  a  century  more  to  attain  to  a  clear  conception 
of  the  theory  of  meteoric  phenomena  as  now  understood. 
It  has  been  shown  by  the  researches  of  H.  A.  Newton,* 
Schiaparelli,  Le  Verrier,  Peters,  Adams,  Weiss,  and  others, 
that  the  meteors  which  fall  within  our  atmosphere  at  regu- 
lar periods,  in  August  and  November,  are  derived  from 
swarms  of  meteoric  bodies  revolving  about  the  sun  in 
orbits  which  intersect  that  of  the  earth.  (See  Figure  5.) 
The  source  of  the  August  meteors  is  believed  to  be  a  cos- 
mical  cloud  forming  a  ring  around  the  sun.  The  aphelion 
of  this  ring  is  1,732  million  miles  beyond  the  orbit  of  Nep- 
tune, f  The  plane  of  the  ring,  or  more  properly,  ellipse,  is 
inclined  at  an  angle  of  64°  3'  to  the  plane  of  the  earth's 
orbit,  and  its  orbital  motion  is  contrary  to  that  of  the 
earth.  The  November  shower  occurs  once  in  thirty-three 
years;  and  hence,  though  the  meteoric  orbit  must  intersect 
that  of  the  earth,  so  that  the  earth  passes  it  annually,  the 
meteors  do  not  stretch  in  a  continuous  ring  around  their 
orbit.  From  the  fact  that  the  meteoric  belt  is  intercepted 
by  the  earth  only  once  in  thirty-three  years,  it  was  shown 
by  Professor  Newton  that  in  33£  years  the  swarm  must 
make  one  revolution,  or  32^,  34^,  65-|  or  67^  revolutions; 
and  that,  to  test  which  of  these  is  the  correct  number,  we 
must  investigate  the  possible  influence  of  the  several 
planets  upon  the  movements  of  the  swarm.  The  investi- 
gation was  made  by  Schiaparelli  of  Milan,  and  about  the 
same  time,  by  Professor  Adams  of  England;  and  it  was 
thus  demonstrated  that  the  33j  years  period  is  the  only 
one  which  satisfies  all  the  conditions.^  On  this  theory  of 

*Sec  Professor  Xewton's  remarkable  succession  of  contributions  to  our 
knowledge  of  the  phenomena  of  meteorites,  and  his  sagacious  discussions  of 
these  phenomena,  and  inferences  from  them,  in  the  successive  volumes  of  the 
American  Journal  of  Science,  from  1861  to  1873. 

tThis  is  based  on  Oppolzer's  determination  of  a  period  of  134  years,  and  is 
obtained  by  Kepler's  third  law.  But  the  period  is  not  accurately  known. 

*  Sir  William  Thompson,  Address  at  Edinboro  Meeting  British  Association, 
Amer.  Jour.  Sci.,  Ill,  ii,  289,  Oct.  1871. 


18  COSMICAL    DUST. 

the  orbital  period  of  the  meteoric  cloud,  it  is  apparent 
that  it  stretches  for  a  long  distance  along  its  orbit,  since 
it  is  intercepted  by  the  earth  on  the  two  Novembers  fol- 
lowing the  principal  shower,  though  the  meteoric  fall  is 
greatly  diminished  at  the  second  and  third  intersections. 
Assuming  the  meteoric  period  to  be  thirty-three  years,  the 
cosmic  cloud  must  therefore  stretch  over  one-eleventh  of 
the  whole  orbit.  The  motion  of  this  cloud  is  also  retro- 
grade; the  inclination  of  the  orbit  is  14°  41',  and  its 
major  axis  is  ten  and  one-third  times  the  mean  diameter  of 
the  earth's  orbit.  The  node  or  point  of  intersection  with 
the  earth's  orbit  has  a  motion  of  52". 4  annually  in  the 
direction  of  the  meteoroidal  motion.  This  meteoric  orbit 
is  therefore,  like  the  other,  similar  to  that  of  a  comet;  and, 
if  it  were  less  inclined  to  the  ecliptic,  would  probably 
serve  as  a  source  of  meteoric  showers  to  Mars  and  the 
Asteroids. 

The  relations  of  these  two  principal  meteoroidal  orbits 
to  the  solar  system  are  intended  to  be  illustrated  by  the 
diagram,  Figure  5.  The  orbits  of  the  earth,  Jupiter, 
Saturn.  Uranus  and  Neptune  are  here  supposed  to  lie  in 
one  plane,  and  are  so  situated  that  the  eye  takes  a  per- 
spective view  across  the  plane.  The  relative  magnitudes 
of  the  orbits  are  not  accurately  represented,  and  Neptune's 
orbit  is  shown  only  in  very  small  part.  The  earth's  orbit 
is  so  placed  that  the  major  axis  does  not  correspond  with 
the  longest  dimensions  shown  in  the  perspective.  The 
same  is  true  of  the  other  orbits.  The  extremities  of  the 
earth's  major  axis  show  approximately  the  positions  of  the 
earth  at  the  solstices,  June  21st  and  December  21st.  The 
arrows  show  the  directions  of  the  motions  represented  in 
the  diagram. 

The  orbit  of  the  November  swarm  of  meteoroids  is 
shown  as  having  an  angle  of  14°  41'  with  the  plane  of  the 
Earth's  orbit.  The  greater  part  of  this  orbit  lies  below  the 


METEORS. 


19 


FIG.  5.   ILLUSTRATING  THE  POSITIONS  OP  THE  AUGUST  AND  NOVEMBER 
METEOROIDAL  SWARMS. 


20  COSMICAL    DUST. 

plane  of  the  ecliptic.  The  motion  of  the  swarm  is  nearly 
opposed  to  the  Earth's  motion.  The  swarm  reaches  its  peri- 
helion a  little  before  it  crosses  the  Earth's  orbit  on  Novem- 
ber 14.  The  Earth  passes  on,  after  the  crossing,  to  the 
winter  solstice  and  beyond.  The  train,  meantime,  is  trail- 
ing across  the  path  of  the  Earth  at  the  November  point. 
It  is  of  such  length  that  it  continues  to  trail  across  until 
the  Earth  has  reached  the  November  point  again  and 
again.  It  is,  therefore,  many  millions  of  miles  in  length. 
The  aphelion  point  of  this  meteoroidal  orbit  is  a  little  more 
remote  than  the  orbit  of  Uranus. 

Similarly,  the  orbit  of  the  August  swarm  of  meteor- 
oids  is  represented  as  having  an  angle  of  64°  3'  with  the 
plane  of  the  Earth's  orbit.  It  is,  therefore,  turned  up  so 
that  the  view  presented  in  the  figure  is  much  less  oblique, 
and  the  orbit  appears  very  broad.  The  longer  axis  of  the 
orbit,  however,  is  greatly  foreshortened,  and  the  two 
branches  must  be  conceived  as  retreating  into  the  far 
distance,  a  little  to  the  left  of  the  direction  of  the  line  of 
sight.  The  aphelion,  which  is  one  thousand  seven  hun- 
dred and  thirty-two  million  miles  beyond  the  orbit  of 
Neptune,  is  almost  included  in  the  diagram.  This  swarm 
is  four  million  miles  broad,  and  reaches  quite  around  its 
orbit,  though  the  meteoroidal  bodies  are  not  uniformly 
distributed.  Hence  the  August  shower  is  of  annual 
occurrence,  while  the  brilliancy  of  the  display  is  very 
variable. 

Several  other  remarkable  cosmic  clouds  have  been  recog- 
nized, and  the  following  table  of  the  best  established  has 
been  arranged  from  the  Aniniaire  clu  litireati  des  L«n</!- 
t  titles  for  1881.  The  table  gives  the  epoch,  right  ascen- 
sion and  declination  of  the  principal  radiant  point  in  each 
cloud. 


METEORS. 


TABLK    OF    METEOROIDAL    SWARMS. 


Radiant  Points. 

EPOCHS. 

I. 

II.               III. 

IV. 

R.A 

Dec. 

R.A 

Dee.  R.A 

Dec. 

R.A 

Dec. 

I 

Jan.  2  to  3.     .  .    . 

238° 

+45° 

IT 
III 

Apr.  12  to  13..    . 
Apr.  19  to  23..    . 

273° 
267° 

+25= 
+35° 

238° 

-30° 

225C 

+52° 

204° 

-18° 

IV 

July  26  to  29  .  .    . 

342° 

-34° 

V 

Aug.  9  to  14  .  .    . 

43° 

+57° 

345C 

+50°  294° 

+52  > 

9° 

-19° 

VI 

Oct.  19  to  25  .  .    . 

74° 

+25° 

95° 

+15°  112° 

+29° 

VII 

Nov.  13  to  14.  . 

148° 

+24° 

53° 

+32° 

279° 

+56° 

VIII 

Nov.  271o29  ... 

25° 

+45° 

IX 

Dec.  6  to  13  

105° 

+30" 

149° 

+4,. 

NOTES.  Swarm  II  is  perhaps  only  a  stray  portion  of  III.  Of 
the  latter  the  Chinese  records  mention  many  recurrences,  and  the 
swarm  is  thought  connected  with  the  Comet  I  1860.  Swarm  IV  is 
spread  over  the  whole  heaven  of  the  northern  hemisphere,  but  in 
the  southern,  the  principal  radiant  is  as  indicated.  Swarm  V  is 
known  as  the  Swarm  of  St.  Lawrence,  also  as  Perseids.  Accord- 
ing to  J.  J.  Schmidt,  there  are  not  less  than  forty  radiant  points  in 
all.  These  meteors  are  connected  with  the  Comet  III  1862.  Swarm 

VI  has  many  radiants  indicated  in  the  course  of  many  years.    Swarm 

VII  is  known  as  the  Leonids,  which  revolve  in  the  orbit  of  the 
Comet  I  1866.     Swarm  VIII  is  in  connection  with  the  Comet  of 
Biela-Gambart,  which  in  1872  gave  origin  to  a  fine  display  of  mete- 
ors.    Swarm  IX  is  composed  of  small  bodies,  but  exceptionally  brill- 
iant.    It  possesses  numerous  radiant  points. 

Here  arc  given  the  positions  of  twenty  important  radi- 
ant points,  each  of  which  may  really  appertain  to  a  distinct 
swarm,  though  exhibited  simultaneously  with  other  radi- 
ants. But  besides  these  are  numerous  others;  and  if  each 
separate  radiant  corresponds  to  a  distinct  swarm,  moving 
in  a  distinct  orbit,  we  have  knowledge  of  more  than  a  hun- 
dred meteoroidal  orbits  which  pass  in  close  proximity  to 
the  earth's  orbit.  This,  in  the  opinion  of  some  physicists, 


22  COSMICAL   DUST. 

is  the  fact.  In  truth,  there  is  scarcely  a  night  in  the  year, 
as  every  one  can  testify,  when  some  meteors  may  not  be 
seen.  If  these  bodies  are  generally  connected  with  swarms, 
large  or  small,  there  is  scarcely  a  night  when  the  earth's 
path  is  not  intercepted  or  grazed  by  a  meteoroidal  train. 
A  similar  number  must  pass  during  the  day;  and  we 
should  thus  have  indications  of  over  seven  hundred  passing 
annually  in  close  proximity  to  the  earth,  each  of  which 
might  be  794,000  miles  in  diameter.  These  trains  are  as 
clouds  of  sand  floating  in  space,  but  describing  regular 
orbits  about  the  sun.  The  constituent  bodies  may  be 
conceived  as  possessing  all  dimensions,  from  a  molecule 
of  matter  to  the  size  of  an  asteroid. 

Now,  let  it  be  borne  in  mind  that  the  cosmic  clouds  of 
whose  existence  we  have  learned,  are  only  such  as  have 
orbits  intersecting  or  grazing  that  of  the  earth.  Let  it  be 
remembered,  too,  that  of  all  meteoroidal  orbits  intersecting 
that  of  the  earth,  only  such  can  be  revealed  as  are  traversed 
by  the  meteoroidal  swarm,  at  the  point  of  intersection,  at 
the  same,  time  that  the  earth  happens  to  be  passing  the 
same  point.  How  many  must  there  be  located  in  such  po- 
sitions as  not  to  be  brushed  by  the  earth's  atmosphere,  or 
impressed  by  the  earth's  attraction.  The  intersection  of 
one  of  these  meteoroidal  orbits  by  that  of  the  earth  is  al- 
most like  striking  a  solitary  line  by  a  random  shot  in  infi- 
nite space.  The  interception  of  a  swarm  is  like  hitting  a 
particular  point.  Millions  of  chances  against  it.  How 
many  meteor  swarms  have  we  a  right  to  assume  as  proba- 
bly sweeping  in  all  conceivable  directions -at  all  conceivable 
distances,  within  at  least  the  limits  of  our  system,  about 
this  central  sun?  Could  our  vision  be  unsealed,  we  should 
behold  the  infinite  firmament  dotted  with  meteors  hurrying 
to  and  fro,  as  snow-flakes  in  the  wildest  wintry  storm. 

From  this  survey  of  facts  and  theories  it  appears  mani- 
fest that  the  "dust  of  time"  comes  down  to  us  out  of  the 


ZODIACAL   LIGHT.  23 

interplanetary  spaces.  These  meteoric  matters  are  samples 
of  the  stuff  which  exists  in  the  far  regions  where  the  stars 
are  shining.  It  comes  to  us  and  we  handle  it  and  investi- 
gate it,  and  find  it  exactly  like  the  stuff  from  which  our 
world  is  made.  We  are  not  isolated,  as  we  had  thought, 
from  the  starry  realm.  Even  the  meteors  are  messengers  — 
flaming  messengers — bringing  us  these  tiding-s  from  dis- 
tant provinces,  and  assuring  us  that  the  government  whose 
details  are  administered  upon  our  earth  is  loyally  recog- 
nized in  the  regions  lying  on  the  distant  verge  of  the  visi- 
ble universe. 

§  2.   THE  ZODIACAL  LIGHT. 

Secondly,  the  ZODIACAL  LIGHT  yields  evidence  of  cos- 
mical  matter  floating  in  space.  This  is  a  faint  yellowish 
light  which  rises  like  an  ill-defined  cone  from  the  western 
horizon  just  after  sun-set  during  winter  and  spring,  and 
from  the  eastern  horizon  just  before  sun-rise  in  summer 
and  autumn.  It  extends  very  nearly  in  the  plane  of  the 
ecliptic;  and  hence,  when  the  direction  of  the  ecliptic  is 
strongly  inclined  toward  the  horizon,  this  faint  light  is 
obscured  by  the  atmosphere,  and  remains  unnoticed.  It 
sometimes  extends  nearly  to  the  zenith,  and  there  are 
many  accounts  of  its  appearance,  especially  in  tropical 
latitudes,  in  the  western  and  eastern  horizons,  at  the  same 
time,*  though  the  brightness  is  much  less  in  the  horizon 
opposite  the  sun. 

Polariscopic  study  of  the  light  shows  it  to  be  polarized 

*For  a  valuable  mass  of  observations  ou  the  zodiacal  light,  with  a  large 
number  of  graphical  illustrations,  see  Chaplain  George  Jones'  memoir  in  Report 
U.  8.  Japan  Expedition,  vol.  iii,  as  also  a  brief  statement  in  Astronomical  Jour- 
nal No.  84,  and  Amer.  Jour.  Set.,  II,  xx,  138-9.  For  other  data  see  M.  Houzeau's 
memoir  in  Astronomische  Nathrichten,  1843,  and  the  valuable  paper  of  Prof  D. 
Olmsted  in  Am.  Jour.  Sd.,  II,  xii,  309-22,  embracing  the  best  graphical  delinea- 
tion known  to  the  present  writer.  For  historical  and  critical  notes  see  Hum- 
boldt :  Cosmos,  Otte  translation,  i,  137-44. 


24  COSMICAL   BUST. 

in  a  plane  passing  through  the  sun.  The  amount  of 
polarization  is  15  to  20  per  cent.  This  result  shows  that 
the  light  is  derived  from  the  sun,  and  is  reflected  from 
solid  matter  consisting  of  small  bodies  apparently  not 
differing  in  their  nature  from  terrestrial  minerals.*  Spec- 
troscopic  study  of  the  light  leads  to  the  same  conclusion. 
Its  spectrum  is  continuous,  and  is  sensibly  the  same  as 
that  of  faint  sunlight  or  twilight,  f  It  seems  well  settled, 
therefore,  that  we  have  in  this  phenomenon  a  true  exam- 
ple of  cosmical  dust  floating  in  space  and  rendered  lumi- 
nous, like  the  dust  rising  from  our  streets,  by  the  reflection 
of  solar  light.  This  happens  to  be  very  exactly  the  same 
view  promulgated  by  Dominicus  Cassini  in  1730,  who  was 
the  first  to  devote  elaborate  study  to  this  phenomenon. 

The  arrangement  of  these  cosmical  matters  in  relation 
to  the  sun  and  the  earth  has  been  much  discussed.  La- 
place concluded  that  they  could  not  belong  to  the  atmos- 
phere of  the  sun,  since  the  form  is  far  too  lenticular  for  a 
body  rotating  no  more  rapidly  than  the  sun.  \  Still,  he 
suggests,  as  Cassini  had  done  at  an  earlier  date,  that  the 
matter  of  the  zodiacal  light  may  surround  the  sun  as  a 
ring;  and  he  suggests,  also,  an  origin  for  it,  in  conformity 

*  A.  W.  Wright,  Am.  Jour.  Sci.,  Ill,  vii,  451-9 

t  A. "W.  Wright,  Am.  Jour.  Sci.,  III,  viii,  39-46.  Some  other  observers,  nota- 
bly MM.  Respighi  and  Angstrom,  have  reported  a  bright  yellow  line  in  the  spec- 
trum; but  Prof.  Wright  found  it  present  only  when  the  aurora  borealis  was 
displayed,  ami  was  never  seen  when  the  aurora  was  absent.  Father  Secchi's 
experience  was  the  same.  See,  also,  observations  by  Prof.  Piazzi  Smyth, 
Monthly  Notices,  Roy.  Astr.  Soc.,  June  1872,  p.  277,  and  M.  Liais,  Comptes  Ren- 
dtis,  Ixxiv,  262,  1872.  See  further,  R.  A.  Proctor,  Monthly  Notices,  xxxi.  No.  i, 
Nov.  11,  1870. 

J  Laplace :  Systeme  dit  Monde,  Liv.  iv,  ch.  x,  ed.  18 24,  p.  270.  Nevertheless 
Father  Secchi  says,  in  view  of  the  changes  in  the  color  of  the  zodiacal  light,  at 
the  time  of  perihelion  passage  of  the  comet  of  1843,  ••  cela  prouverait  done  que 
cette  lumiere  n'est  qne  Vatmospherc  solaire,  et  non  pas  un  anneau  de"tnche'"(£« 
Sol-iil,  2d  ed.,  ii,  433).  It  is  generally  represented  that  Kepler  had  thought  the 
zodiacal  light  to  be  a  portion  of  the  sun's  atmosphere,  but  Humboldt  maintains 
(Cosmos,  i,  140,  note)  that  this  "limbus  circa  solem,  coma  lucida"  has  no  refer- 
ence to  this  phenomenon. 


ZODIACAL   LIGHT.  25 

with  his  celebrated  hypothesis  respecting  the  origin  of  the 
planets.  "  If,"  he  says,  "in  the  zones  abandoned  by  the 
atmosphere  of  the  sun,  there  existed  any  molecules  too 
volatile  to  unite  with  each  other  or  with  the  planets,  they 
ought,  in  continuing  to  circulate  about  that  body,  to  pre- 
sent all  the  appearances  of  the  zodiacal  light,  without 
offering  any  sensible  resistance  to  the  various  bodies  of 
the  planetary  system,  for  the  reason  either  of  their  ex- 
treme tenuity,  or  because  their  motion  is  almost  exactly 
the  same  as  that  of  the  planets  which  encounter  them."  * 

Whether  this  is  a  correct  conception  of  the  zodiacal 
light  or  not,  it  is  generally  agreed  that  the  phenomenon 
arises  from  a  ring  of  meteoroidal  bodies  encircling  the  sun, 
nearly  in  the  plane  of  the  ecliptic,  and  probably  rotating 
like  the  rings  of  Saturn.  But  considering  that  the  phe- 
nomenon has  so  frequently  been  witnessed  in  the  east  and 
west  at  the  same  time,  it  is  necessary  to  assume  that  while 
most  of  the  matter  lies  within  the  earth's  orbit,  some  por- 
tion extends  beyond  that  limit.  Accordingly,  the  earth 
moves  within  the  assemblage  of  particles.  Consequently, 
unless  they  have  precisely  the  same  velocity  as  the  earth, 
they  must  by  their  collisions  offer  a  resistance  to  the 
earth's  motion.  The  entrance,  then,  of  these  zodiacal 
molecules  into  the  earth's  atmosphere  might  present  me- 
teoric phenomena. 

A  different  location  of  this  annulus  is  maintained  by 
others.  Rev.  George  Jones,  before  cited,  argues  that  the 
appearance  of  the  light  in  both  horizons  at  the  same  time 
is  evidence  that  the  annulus  surrounds  the  earth.  Profes- 
sor Stephen  Alexander  f  for  similar  reasons  rejects  all 
heliocentric  theories,  and  maintains  that  the  annulus  is  an 

*  Laplace:  Systlme  du  Monde,  Xote  vii,  415-6.  M.  Roche  also  regards  the 
matter  of  the  zodiacal  light  as  a  remnant  of  the  primitive  nebula. 

t  S.  Alexander,  Smithsonian  Contributions,  xxi,  No.  i,  68.  In  opposition  to 
the  geocentric  theory  gee  F.  A.  P.  Barnard,  Am.  Jour.  Sci.,  II,  xxi,  217-37;  and 
Commander  Charles  Wilkes,  Proc.  Amer.  Assoc.  1857,  83-92,  399-401. 


26  OOSMICAL   DUST. 

appurtenance  of  the  earth,  lying  nearly  in  the  plane  of 
the  moon's  orbit,  and  that  it  is  girdle-shaped  instead  of 
discoid.  He  calls  it  "  a  nebulous  girdle  revolving  around 
the  earth  in  the  same  time  and  general  direction  with  the 
moon."  He  compares  it,  like  Chaplain  Jones,  with  the 
dusky  ring  of  Saturn,  though  differing  in  shape.  The  very 
unequal  intensity  of  the  light  in  the  horizon  opposite  the 
sun  is  a  fact  at  variance  with  the  geocentric  theory.  The 
original  conception  of  Cassini  and  Laplace  seems  most 
conformable  with  all  the  facts;  and  there  is  much  reason 
in  the  supposition  also,  that  this  ring  is  a  remnant  of  the 
primitive  nebula,  detached  according  to  the  principles 
which  I  shall  hereafter  explain.  One  circumstance,  how- 
ever, indicates  that  this  phenomenon  may  be  something  of 
modern  origin;  since,  of  all  the  acute  observers  of  the 
heavens  in  ages  past,  from  the  Babylonians  to  Tycho  and 
Kepler,  none  make  any  allusion  to  it  before  the  latter  part 
of  the  seventeenth  century.  Childrey,  in  1661,  gives  the 
first  clear  and  unmistakable  mention  of  it.*  If  it  is 
indeed,  a  phenomenon  of  modern  origin,  it  cannot,  of 
course,  be  viewed  as  a  vestige  of  the  work  of  planetarv 
evolution.  We  must  seek  for  some  appropriate  existing 
action  and  process,  and  we  may  direct  our  inquiries  to  the 
seemingly  repulsive  power  exerted  by  the  sun  in  the 
radiant  forms  of  the  solar  corona  and  in  the  tails  of 
comets,  f 

'Childrey:  Britannia  Saconlca,  183,  cited  by  Humboldt. 

tit  may  be  mentioned  as  a  matter  of  interest  that  Prof.  D.  Olmsted  as 
parly  as  1834  (.4m.  Jour,  fici.)  suggested  a  nebulous  body  revolving  around  the 
sun  as  the  source  of  the  November  meteor  shower  of  1&33,  and  he  identified 
this  with  the  xodiacal  lis?ht  in  1851  in  the  memoir  before  cited.  The  same 
suggestion  wns  made  in  183G  by  M.  Biot  as  to  the  r.ebnlar  origin  of  the  meteors. 
Commander  Wllkes  (op.  rif.,  p.  89)  concludes  that  the  zodiacal  light  "is  the 
result  of  the  illumination  of  that  portion  or  section  of  the  earth's  atmosphere 
on  which  the  rays  of  the  sun  fall  perpendicularly." 


COMETS  27 

§  3.     COMETS. 

Thirdly,  the  COMETS  are  now  known  to  be  simply  con- 
glomerations of  cosmical  dust.  These  bodies  are  not,  as 
Kant  and  others  have  supposed,  natives  of  our  system. 
This  is  apparent  when  we  consider  that  their  motions,  save 
the  fundamental  principle  of  motion  in  a  conic  section, 
bear  no  conformity  to  the  rule  of  motions  of  the  planets  and 
satellites.  Comets  approach  the  sun  from  all  conceivable 
directions,  moving  sometimes  nearly  in  the  plane  of  the 
ecliptic,  sometimes  plunging  down  from  the  neighborhood 
of  the  zenith  or  rising  from  the  nadir  or  emerging  into 
visibility  in  the  vicinity  of  either  pole.  From  a  table  of 
300  comets  recently  published  by  Niesten,*  it  appears  that 
in  regard  to  the  inclinations  of  their  orbits  67  ranged  be- 
tween 0  and  30°;  113  between  30°  and  60°,  and  110 
between  60°  and  90°.  Comets  move  accordingly  in  all 
directions  around  the  sun.  About  half  of  all  the  comets 
known  possess  a  retrograde  motion;  though  most  of  the 
comets  of  short  period  possess  direct  motion — a  circum- 
stance which,  as  will  be  shown,  seems  to  be  due  to  the 
perturbative  influence  of  planets  moving  in  a  common  di- 
rection from  west  to  east.  That  they  are  foreigners  in  our 
system  is  apparent,  also,  from  the  fact  that  only  a  small 
portion  of  the  comets  which  visit  us  are  known  to  move  in 
elliptical  orbits.  That  is,  the  great  majority  never  return 
to  describe  another  circuit  about  our  sun.  They  approach 
from  unknown  regions,  and  retire  to  regions  equally  un- 
known. It  is  further  apparent  from  the  non-conformity 
of  comets  to  the  chemical  constitution  of  the  sun  and 
planets.  We  only  know  that  carbon,  apparently  combined 
with  hydrogen,  exists  in  the  substance  of  some  of  them. 
It  may  be  considered,  however,  very  doubtful  whether  we 

*  Niesten:  Table  des  Cometes,  in  Annuaire  de  1'Observatoire  Royal  de 
Bruxelles. 


28  COSMTCAL   DUST. 

are  in  a  position  to  affirm  or  deny  the  presence  of  any 
element. 

Of  the  thirty-eight  comets,  believed  to  revolve  in  ellip- 
tic orbits,  only  twelve  have  been  seen  at  more  than  one 
return. 

The  following  is  a  list  of  the  principal  comets  of  short 
period.  Those  marked  with  a  star  have  been  ssen  at  more 
than  one  return: 

COMETS    OF    SHORT    PERIOD. 

Period 
Motion.  yrs. 

*  1.  Eneke's  (Pons,  1818) Direct  3. 288 

2.  Blan pain's  (1819) Direct  4.81 

3.  Burkhardt's  *  (1766  II) Direct  5.025 

*  4.  Tempel's  (1873   II) Direct  5.066 

5.  De  Vico's  (1844  I) . .   .  Direct  5.459 

*  6.  Brorsen's  (1846  III) Direct  5.473 

*  7.  Winnecke's  (1858  II) Direct  5.727 

8.  Pigott's(1783) .  Direct  5.888 

*  9.  Tempel's  (1867  II) Direct  5.905 

*  10.  Swift's  (1880  IV) Direct  ?6. 

*11.  Biela'sf( Feb.  1826}    Direct  6.619 

*  12.  D'Arrest's  (June  27,  1851) Direct  6.664 

*  13.  Faye's  (Nov.  22,  1843) Direct  7.412 

*  14.  Denning's  (F,  Oct.  4,  1881) Direct  8.8567 

15.  Peter's  (1846  V) ?  Direct  12.85 

*  16.  Turtle's  (Jan.  4,  1858) Direct  13.81 

17.  Tempel's  (1866 1.  "Comet  of  Nov.Meteors")  Retrograde  33.18 

18.  Stephan's  (1867  I) Direct  33.62 

19.  Westphal's  (July  24,  1852) Direct  60.03 

20.  PODS'  (July  20,  1812) Direct  70.69 

21.  De  Vico's  (1846  III) Direct  73.25 

22.  Gibers' (March  6,  1815) Direct  74.05 

23.  Brorsen's  (1847V)....'. Direct  74.97 

*  24.  Halley's Retrograde  76.30 

25.  (1862  III,  "Comet  of  Aug.Meteors")  Retrograde  ?  124. 

'Thought  perhaps  identical  with  \Yinnecke°8. 

t  Not  seen  since  1852.  Supposed  to  have  struck  the  earth  at  the  end  of 
November,  1872,  and  to  have  caused  the  memorable  meteoric  display  at  that 
date.  This  is  Swarm  viii  of  the  preceding  Table. 


COMETS.  29 

It  has  been  conjectured  that  the  great  southern  comet, 
I  1880,  is  the  same  as  the  great  comet  of  1843.*  Donati's 
comet  of  1858  has  a  calculated  period  of  2,100  years;  the 
comet  of  1811  and  the  great  comet,  B  1881,  periods  of 
3,000  years;  that  of  1G80  is  expected  to  be  absent  8,814 
years.  Coggia's  comet,  IV  1874,  has,  according  to  Dr. 
Hepperger,  a  period  of  13,708  years,  while  the  comet  of 
July,  1844,  has  a  calculated  period  of  100,000  years. 
These  long  periods,  however,  are  exceedingly  uncertain. 
The  elliptic  character,  even,  of  the  orbits,  is  not  in  all  cases 
fully  established.  Even  when  really  elliptic,  moderate 
perturbations  may  cause  great  change  in  the  periods. 

The  relative  position  of  the  great  comet  of  1881f  is 
shown  in  perspective  in  Figure  5.  The  point  of  view  is 
such  that  the  plane  of  the  cometary  orbit  is  presented 
quite  obliquely,  and  the  spectator  contemplates  it  from 
below.  The  reader  must  therefore  conceive  the  lower 
branch  of  the  orbit  much  more  remote  than  the  upper. 
P,  below  the  ecliptic,  denotes  the  perihelion  point  of  the 
comet,  and  N,  the  node  where  it  passed  from  the  south  to 
the  north  side  of  the  ecliptic.  This  diagram  explains  why 
the  comet  was  discovered  in  May  in  the  southern  hemi- 
sphere, but  was  not  seen  in  the  northern  hemisphere  till 
four  weeks  later.  In  May  it  was  below  the  horizon  of 
northern  observers;  and  later,  when  it  had  risen  above 
their  horizon,  it  was  too  nearly  in  the  direction  of  the  sun 
to  be  seen.  Meantime  it  passed  its  perihelion,  and  when 
first  seen,  June  20,  in  the  northern  hemisphere,  it  was 
already  receding  from  the  earth  and  the  sun.  The  dia- 
gram explains,  also,  why  northern  observers  saw  this 
comet  in  the  neighborhood  of  the  north  star,  or  the  region 

*  Swift:  Science  i,  258. 

t  Comet  B  1881,  discovered  by  Tebbutt  in  New  South  Wales,  May  22,  and 
rediscovered  in  the  northern  hemisphere,  June  JO,  by  G.  W.  Simmons,  then  at 
Morales,  Mexico.    See  an  illustrated  article  About  Cometsby  A.  N.  Skinner  in  . 
Popular  Science  Montldy,  xix,  790-5,  Oct.,  1881. 


30  COSMICAL    DUST. 

toward  which  the  axis  of  the  earth  is  directed  ;  and  why  it 
continued  in  that  neighborhood  as  it  receded  during  July, 
though  slowly  diverging  from  the  direction  of  the  polar 
star.  The  diagram  also  shows  why  this  gradual  diver- 
gence was  to  an  observer  in  the  evening,  toward  the  left 
from  the  pole,  in  the  direction  of  the  sun.  This  comet 
remained  visible  for  seven  months,  and  could  be  faintly 
seen  as  late  as  Christmas,  1881.  It  was  then  in  the  con- 
stellation Cepheus.  It  was  even  visible  telescopically  one 
or  two  months  later.  The  great  comet  of  1882  will  not  be 
forgotten  by  the  present  generation.  It  was  first  seen 
September  2,  and  continued  visible  to  May  6,  1883,  pass- 
ing over  339^°  of  heliocentric  arc,  leaving  but  20^°  to  be 
completed  during  the  remainder  of  its  orbital  circuit,  sup- 
posing it  to  be  periodic.  The  great  comet  of  1680  was 
visible  through  345°  of  arc,  from  November  14,  1680  to 
March  19,  1681. 

The  great  comet,  1882  b,  just  mentioned,  is  worthy  of 
more  particular  notice.  It  was  seen  at  Auckland,  N.  Z., 
September  2,  1882  ;  at  the  Cape  of  Good  Hope,  by  Finlay, 
September  6,  and  at  Rio,  by  Grills,  September  12.  In 
approaching  perihelion,  it  was  seen  by  Finlay  and  others 
to  pass  before  the  sun's  disc,  though  wholly  invisible 
during  the  transit.  After  perihelion,  the  nucleus  was  seen 
to  begin  to  divide,  as  early  as  September  28.*  On  Octo- 
ber 5,  two  nuclear  fragments  were  seen  at  Strasbourg. 
Three  fragments  were  reported  at  the  same  date  by  Bar- 
nard at  Nashville,  Tennessee,  and  Wilson,  at  Cincinnati; 
while  from  Guatemala  five  distinct  bodies  were  reported. f 
By  October  12,  four  separate  condensations  were  distinctly 
seen.t  On  October  14,  Mr.  E.  E.  Barnard,  of  Nashville, 

*  Nature,  xxvii,  150,  with  views  for  September  16  and  October  30.  Also  note, 
ibid,  161. 

t  Nature,  xxvii,  113. 

JW.  Dobcrck,  at  Markreo  Observatory.  (Nature,  xxvii,  129.  with  illustra- 
tions.) E  S.  Holdi-n  saw  at  Madison,  \Vi*.,  three  condensations  (Amer.  Jour. 
Sci.,  Ill,  xxiv,  435,  Nature,  xxvii,  246). 


COMETS.  31 

found,  to  the  south  of  the  comet,  "a  large  distinct  comet- 
ary mass  fully  15'  in  diameter,  and  a  similar,  but  less 
bright  object  close  behind  this,  their  borders  touching, 
and  on  the  opposite  side  of  the  first,  a  third  fainter 
mass.  The  three  were  almost  in  a  line  east  and  west. 
More  of  these  cometary  masses  were  found  toward  the 
south-east.  There  were  at  least  six  or  eight  within  about 
6°  south  by  west  from  the  head  of  the  great  comet." 
They  were  not  afterward  seen.*  Dr.  Schmidt,  of  Athens, 
had  reported  a  detached  cometary  mass  at  an  earlier  date.f 
On  January  27,  Mr.  Ainslie  Common,  of  Baling,  "saw  the 
nuclear  part  of  the  comet  larger  but  less  bright  than  pre- 
viously, and  resolved  into  a  string  of  brightish  points,  the 
second  and  third  of  which  were  much  the  brightest."  A 
sketch  by  Mr.  Common  showed  five  points  of  condensa- 
tion. |  The  separation  of  the  nucleus  seems  to  have  con- 
tinued as  long  as  the  comet  remained  under  observation. 
These  facts  are  significant,  and  appear  to  have  an  important 
bearing  on  the  genetic  connection  of  comets  and  meteors. 
The  calculations  of  Chandler  give  this  comet  an  orbit  of 
4,070  years  with  retrograde  motion.  According  to  Frisby, 
its  period  is  794  years ;  according  to  Kreutz,  843  years  ; 
according  to  Morrison,  652^  years. §  A.  S.  Atkinson,  of 
Nelson,  N.  Z.,  reports  it  visible  to  the  naked  eye  as  late  as 
February  28,  1883,  and  with  telescopes,  until  May  6.  || 

Comets  generally  present  a  nucleus,  a  coma  of  diffused 
light  surrounding  the  nucleus,  and  a  long  tail,  generally 
turned  away  from  the  sun,  somewhat  curved  backwards, 
and  having  a  well-defined  anterior  border,  while  the  pos- 

*  Nature,  xxvii,  400. 

i  Astronomisthf  Nachrichten,  No.  2,468,  Nature,  xxvii,  20-1. 

J  Nature,  xxvii,  400.  Something  quite  similar  had  been  observed  Nov.  15.7 
by  W.  C.  Winlock  at  Washington.  (Nature,  xxvii,  129,  figure.) 

§  Nature,  xxvii.  300. 

|  Nature,  xxviii,  225,  July  5,  1883.  On  this  comet  see  the  important  lecture 
of  Prof.  Scbiaparelli,  reported  in  Nature,  xxvii,  533-4. 


32  COSMIC  A  L    DUST. 

terior  border  gradually  fades  off  into  space.  The  tenuity 
of  all  parts  of  the  comet  is  such  that  stars  of  the  tenth 
and  eleventh  magnitudes  have  been  seen,  not  only  through 
the  expanded  portion  of  the  tail,  but  through  the  most 
condensed  portion,  and  even  through  the  nucleus  itself. 
From  these  facts  it  is  apparent  that  the  amount  of  matter 
in  a  comet  is  generally  inconsiderable.  This  is  demon- 
strated by  the  fact  that  the  comet  of  1770  passed  amongst 
the  satellites  of  Jupiter  without  causing  the  slightest  dis- 
turbance in  their  motions.  The  comet,  on  the  contrary, 
was  thrown  into  a  totally  different  orbit.  Similarly,  the 
comet  of  1861  actually  came  into  contact  with  the  earth 
on  the  30th  of  June  of  that  year,  and  the  human  race  was 
not  annihilated.  Indeed,  the  only  indication  of  the  start- 
ling event  was  a  peculiar  phosphorescence  of  the  atmos- 
phere. According  to  the  accepted  relation  between 
comets  and  periodic  meteor  showers,  it  may  be  said  the 
earth  comes  in  contact  with  a  comet  on  every  occasion 
of  such  displays. 

In  connection  with  the  evidences  of  the  extreme  tenuity 
of  comets,  may  be  mentioned  the  parting  of  Biela's  comet 
while  actually  under  observation,  in  1845.  On  the  26th  of 
November,  it  was  a  faint  nebulous  spot,  not  perfectly 
round,  and  with  an  increased  central  density.  On  the 
19th  of  December  it  was  more  elongated;  on  the  29th,  it 
had  parted.  For  three  months  the  twin  comets  were  traced 
with  a  gradually  widening  interval  between  them.  Thus 
they  departed  from  view  on  their  appointed  journey  of  6§ 
years.  At  the  end  of  that  period,  in  August,  1852,  the 
twin  comets  reappeared,  but  with  an  interval  increased 
from  154,000  miles  to  1,404,000  miles.  The  pair  were  ex- 
pected again  in  1859  and  1866;  but  since  1852  they  have 
never  put  in  an  appearance.  Some  planet  has  turned  them 
into  an  orbit  so  changed  as  to  be  unidentifiable,  or  their 
substance  has  passed  into  some  other  condition  of  exist- 


COMETS.  33 

ence.  The  nucleus  of  the  great  comet  of  1882  exhibited 
a  distinct  tendency  to  separate  into  three  or  four  parts. 
It  remained  visible  till  the  early  months  of  1883,  still  re- 
vealing a  state  of  incipient  division. 

To  what  other  condition  of  existence  is  it  possible  for 
cometary  matter  to  pass?  According  to  Schiaparelli  and 
Oppolzer,  the  meteoric  ring,  or  partial  ring,  is  only  a  de- 
generated comet.  They  suppose  a  train  of  meteoroids 
follows  in  the  path  of  the  comet,  and  that  this  becomes 
continually  more  elongated  until  the  head  overtakes  it. 
Comet  No.  Ill,  of  1862,  has  an  orbit  calculated  by  Oppol- 
zer, which  is  almost  identical  with  the  orbit  of  the  meteoric 
ring  that  yields  the  shooting  stars  of  the  10th  of  August, 
as  calculated  previously  by  Schiaparelli.  This  comet  then, 
Schiaparelli  concludes,  is  merely  the  remains  of  the  origi- 
nal comet  out  of  which  the  meteoric  ring  was  formed.  In 
other  words,  the  comet  and  the  meteoric  ring  are  one  and 
the  same  thing.  This  ring  has  a  major  diameter  of  10,948 
millions  of  miles;  and  at  the  place  where  the  earth  trav- 
erses it  on  the  10th  of  August,  it  must  have  a  thickness 
of  385,800  miles,  since  the  meteoric  display  continues  six 
hours,  and  the  earth  travels  in  August  at  the  rate  of  18 
miles  in  a  second.  The  ring  reveals  itself  as  a  comet  only 
when  its  nuclear  portion  happens  to  be  seen  near  the  node 
when  the  earth  passes.  This  happens  once  in  about  one 
hundred  and  twenty  years. 

By  similar  calculations,  it  has  been  shown  that  the  No- 
vember meteoric  ring,  or  partial  ring,  is  identical  with 
Tempel's  comet,  or  No.  I  of  1866.  This  comet,  according 
to  the  calculations  of  Le  Verrier,  entered  our  system  in 
the  year  126  A.D.,  passing  so  near  the  planet  Uranus  as 
to  be  thrown  into  an  elliptic  orbit  having  a  period  of 
thirty-three  years.*  In  consequence  of  having  its  perihe- 

*This  conclusion  is  rejected  by  Schiaparelli,  in  consequence  of  the  alleged 
insufficiency  of  the  mass.  (Les  Mondes,  xiii,  501,  March  28, 1867. ) 


34  COSMICAL    DUST. 

lion  at  nearly  the  same  point  as  the  earth,  it  becomes  the 
source  of  the  November  meteoric  showers,  which  occur  at 
intervals  of  thirty-three  years. 

The  lost  comet  of  Biela  is  thought  to  reveal  itself  in  a 
train  of  meteoroids  which  was  intercepted  by  the  earth 
November  27,  1872. 

As  to  the  physical  condition  of  these  cometary  groups 
of  cosmical  atoms,  it  appears  from  spectroscopic  observa- 
tions, that  the  coma  and  tail  are  luminous  only  by  reflected 
light,  like  the  zodiacal  ring;  but  the  nucleus  is  proved  to 
be  self-luminous,  either  as  an  incandescent  solid  or  liquid. 
But  it  must  not  be  considered  as  a  continuous  solid  or 
liquid,  since  its  tenuity  is  far  too  great.  The  condition  of 
the  nucleus  then  may  be  comparable  to  that  of  the  cloud 
of  heated  particles  in  the  flame  of  a  lamp,  or  that  of  a 
mist  of  molten  particles;  while  the  tail  may  be  compared 
to  a  cloud  of  dust  illuminated  by  the  rays  of  the  sun. 

That  some  physical  relation  exists  between  comets  and 
meteors  seems  intelligible  and  entirely  probable.  The 
nature  of  that  relation,  as  generally  conceived,  is  such  as 
has  been  stated.  Undoubtedly  the  comets  revealed  to  our 
vision  have  had  a  long  previous  course  of  development. 
There  seems,  at  first,  reason  for  supposing  that  the  meteor- 
oidal  stage  is  an  earlier  rather  than  a  later  phase  in  come- 
tary life.  But  reflection  renders  it  probable  that  the 
regions  of  cometary  evolution  lie  beyond  the  limits  of  a 
planetary  system.  In  the  midst  of  such  a  system,  the 
perturbative  influences,  to  which  cometary  aggregations 
are  so  susceptible,  must  inevitably  be  of  a  destructive 
rather  than  a  constructive  character.  But  I  reserve  the 
fuller  expression  of  my  own  conclusions  until  after  atten- 
tion has  been  directed  to  nebular  phenomena,  and  the  col- 
lateral indications  of  a  vast  stock  of  world  stuff  dissemi- 
nated through  infinite  space. 


35 


4.     SATURNIAN  RINGS. 


Fourthly,  the  SATURNIAX  RIXGS  afford  another  exam- 
ple of  cosmical  dust.  These  have  been  shown  by  Profes- 
sor Peirce  to  be  neither  continuously  solid  nor  liquid. 
This  is  also  apparent  from  the  inconstancy  in  the  number 
and  aspects  of  the  rings,  and  the  great  tenuity  of  the 
marginal  zone  of  one  of  them.  The  matter  of  these  rings 
must  then  be  regarded  as  consisting  of  particles  of  solid 
dust.  They  have,  therefore,  the  constitution  of  a  comet's 
tail,  and  reflect  solar  light  similarly.  They  are  identical 
with  the  meteoric  rings,  save  that  the  constituent  parti- 
cles are  more  closely  crowded,  and  thus  reflect  sufficient 
light  to  become  visible. 

It  is  quite  supposable  that  the  zone  of  the  asteroids,  of 
which  more  than  two  hundred  are  now  known  to  attain 
the  size  of  small  planets,  is  merely  another  meteoric  ring. 
It  is  the  opinion  of  some  astronomers  that  the  number  of 
asteroids  amounts  to  millions.*  This  supposition,  however, 
respecting  the  nature  of  the  asteroidal  group  is  not  enter- 
tained by  the  present  writer. 

§5.     NEBULAE. 

Fifthly,  the  NEBUL.-E  are  other  and  remoter  examples  of 
cosmical  dust,  and  are  every  way  full  of  interest  and  sug- 
gestiveness.  These  mysterious  assemblages  of  matter  de- 
mand our  most  serious  attention.  They  reveal  themselves 
as  faint  clouds  of  luminosity  lying  against  the  dark  blue 
sky.  When  Sir  William  Herschel,  with  his  forty-feet 
reflector,  first  brought  the  nebulae  into  prominent  notice,  f 
he  found  that  many  of  them  resolved  themselves  into  dis- 
tinct points  of  light  under  the  higher  powers  of  his  instru- 
ment. A  nebula,  therefore,  seemed  to  be  an  assemblage 

*The  228th  asteroid  was  discovered  by  Palisa,  August  19,  1882. 

t  It  is  said  that  most  of  his  work  was  done  with  the  twenty- feet  reflector. 


36  COSMICAL    DUST. 

of  thousands  of  stars,  so  far  removed  as  to  be  brought  by 
perspective  into  apparent  close  proximity.  These  he  re- 
garded as  other  firmaments,  removed  incalculable  distances 
beyond  the  outer  limits  of  our  own  firmanent  of  stars,  and 
having  a  life  probably  the  counterpart  of  our  own  firma- 
mental  life.  But  while  thousands  of  the  nebulae  were 
thus  resolvable,  other  thousands  resisted  the  higher  pow- 
ers of  his  instrument,  which  is  said  to  have  magnified  up 
to  six  thousand  diameters.  The  irresolvable  nebulae  Sir 
William  Herschel  conceived  to  be  crude  world-stuff,  out  of 
which  suns  and  planets  were  destined  to  be  made.  This 
idea,  so  consonant  with  the  previous  suggestion  of  Kant, 
was  taken  up  by  Laplace,  and  put  into  the  shape  of  a 
physical  theory,  which  became  known  as  the  "nebular 
hypothesis."  * 

With  the  introduction  of  the  gigantic  reflecting  tele- 
scope of  Lord  Rosse,  fifty-two  feet  in  length,  many  of  the 
nebulae  were  resolved  which  Sir  William  Herschel  had  re- 
garded irresolvable  ;  and  many  hitherto  unseen  nebulas 
were  brought  within  the  range  of  vision.  It  appeared, 
therefore,  that  the  outer  limits  of  the  material  creation 
had  not  been  reached,  and  the  suspicion  was  aroused  that 
all  nebulas  might  be  resolved  if  we  could  apply  unlimited 
telescopic  power.  This  idea  was  antagonistic  to  the  nebu- 
lar hypothesis,  and  the  latter  accordingly  receded  in  favor. 

As  the  power  of  the  telescope  to  reveal  the  constitution 
of  the  nebulae  seemed  to  have  reached  its  limit,  and  the 
prevailing  conviction  was  only  a  presumption  that  all 
nebulas  are  inherently  discrete  or  cluster-like,  we  are  in- 
debted to  the  spectroscope  for  any  further  advance  of 
knowledge  in  this  direction. 

*  Laplace,  however,  does  not  seem  to  have  been  acquainted  with  Kant's 
older  and  most  suggestive  speculations;  but  he  acknowledges  his  indebtedness 
to  Sir  William  Herschel,  in  bringing  to  light  the  actual  existence  of  the  crude 
world-material  which  furnished  the  starting  point  of  Laplace's  speculation. 
The  reader  will  find  a  summary  of  opinions  in  Part  IV  of  the  present  work. 


NEBULA.  37 

The  spectroscope,  invented  by  Bunsen  and  Kirchoff  in 
recent  times,  is  one  of  the  most  marvellously  efficient  in- 
struments for  scientific  research  that  has  ever  been  devised. 
Its  powers  are  magical.  It  seizes  the  slender  ray  admitted 
to  a  darkened  room  through  a  narrow  slit  in  the  window 
shutter,  and  extorts  from  it  the  confession  of  the  nature  of 
its  origin.  It  compels  the  ray  to  write  out  the  names  of 
the  substances  which  enter  into  the  constitution  of  the 
luminous  body  from  which  it  proceeds.  It  compels  it  to 
declare  whether  its  source  exists  as  a  luminous  gas  or 
vapor,  or  as  an  incandescent  solid  or  liquid,  or  as  a  glow- 
ing solid  or  liquid  shining  through  gases  or  vapors.  Such 
revelations  of  the  constitution  and  physical  condition  of 
suns  and  stars  and  nebulre  are  not  alone  surprising;  they 
are  amazing.  A  luminous  body  separated  from  us  by 
hundreds  of  millions  of  miles,  sending  its  light  across 
unexplored  intervals  of  cold  space,  so  remote  that  the 
•light  which  falls  upon  our  eyes  to-night  must  have  left  its 
source  before  Shufu  reared  the  great  pyramid  above  the 
plains  of  Egypt,  has  indited  a  message  which  we  read  in 
the  laboratory,  like  a  letter  delivered  by  post  from  a  friend 
in  another  city. 

And  yet  this,  like  other  magic,  is  simple  when  ex- 
plained. It  all  depends  on  the  undulatory  origin  of  light, 
and  the  inequality  of -the  waves  for  the  different  colors  of 
which  white  light  is  composed.  Every  one  understands 
that  a  ray  of  light  passed  through  an  angle  of  a  prism  is 
decomposed  into  seven  colors  commonly  called  "primary," 
which  range  themselves  in  a  fixed  order  on  a  screen.  The 
decomposition  of  the  white  ray  results  from  the  varying 
refrangibility  of  the  constituent  colors.  The  different 
refrangibilities  result  from  the  different  wave-lengths  of 
different  colors.  The  length  of  a  luminous  wave  varies 
from  about  seven  hundred  and  sixty  millionths  of  a  milli- 
meter at  the  red  end  of  the  spectrum  to  about  three  hun- 


38  COSMICAL   DUST. 

dred  and  ninety-three  millionths  of  a  millimeter  at  the  violet 
end.*  That  is,  the  force  which  is  the  cause  of  the  sensa- 
tion of  light  produces  inconceivably  minute  undulations  in 
some  medium — generally  regarded  the  same  as  the  ethereal 
medium  —  and  these  undulations  are  propagated  at  the 
rate  of  about  one  hundred  and  eighty-five  thousand  miles 
a  second,  entering  the  eye  and  striking  the  retina,  and 
thus  being  followed  by  the  sensation  of  light.  When  the 
undulations  are  of  such  width  that  only  three  hundred  and 
ninety-five  trillions  of  them  enter  the  eye  in  a  second,  we 
experience  the  sensation  of  red  light;  when  they  are  so 
minute  that  seven  hundred  and  sixty-three  trillions  enter 
the  eye  in  a  second,  we  experience  the  sensation  of  violet 
light.  Undulations  of  intervening  amplitudes  give  sensa- 
tions of  other  colors  of  the  spectrum  between  the  red  and 
the  violet. 

Three  classes  01  spectra  are  to  be  distinguished.  1. 
The  Continuous  Spectrum;  2.  The  Bright-line  Spec- 
trum; 3.  The  Dark-line  Spectrum,  If  the  light  proceed 
from  an  incandescent  solid  or  liquid,  the  spectrum  is  con- 
tinuous. It  consists  of  a  series  of  colors  in  their  fixed 
succession,  gradually  shading  into  each  other  as  we  see 
them  in  the  rainbow.  The  substance  of  which  the  incan- 
descent body  is  composed  does  not  materially  affect  the 
spectrum.  Different  substances  merely  give  variations  in 
the  relative  widths  of  the  different  colors. 

If,  however,  the  light  proceed  from  an  incandescent  gas 
or  simple  substance  in  the  state  of  vapor,  the  spectrum 
consists  only  of  a  set  of  bright  lines.  These  occupy  dif- 
ferent positions,  and  display,  accordingly,  different  colors 
of  the  continuous  spectrum.  Now  the  critical  fact  in 
spectroscopic  science  is  this:  The  bright  lines  produced 
by  any  substance  are  always  in  the  same  relative  positions 

*  Solar  radiations  are  traceable  in  greater  wave  lengths  in  the  ultra-red,  and 
in  shorter  wave-lengths  in  the  ultra-violet. 


NEBULJE.  39 

in  the  spectrum.  If  we  employ  a  different  gas  or  vapor, 
we  obtain  a  different  set  of  bright,  colored  lines.  Thus 
hydrogen  gives  a  broad  bright  line  in  the  orange,  and 
narrower  ones  in  the  greenish-blue  and  the  blue.  Sodium 
vaporized  gives  a  broad  line  in  the  yellow,  which,  with 
greater  dispersive  power  of  the  prism-arrangements,  be- 
comes a  double  yellow  line.  Light  proceeding  from  a 
mixture  of  two  or  more  gases  or  vapors  gives  the  lines 
characteristic  of  each.  One  acquainted  with  the  charac- 
teristic lines  of  different  elements  is  able,  on  this  principle, 
to  indicate  what  substances  are  present  in  the  gas  or  vapor 
giving  a  certain  succession  of  bright  lines.  So  constant 
are  the  spectroscopic  characters  of  the  same  substance, 
and  so  exact  and  measurable  the  phenomena,  that  our 
confidence  is  in  no  sense  abated,  even  if  we  know  the 
bright  lines  are  produced  by  an  astronomical  body. 

If,  finally,  the  light  proceed  from  an  incandescent  solid 
.or  liquid  body,  and  be  transmitted  through  a  gas  or  vapor 
at  a  lower  temperature,  we  get  a  colored  spectrum  crossed 
by  dark  lines.  And  now  the  critical  fact  is  this:  The 
dark  lines  occupy  the  same  relative  positions  in  the  spec- 
trum as  the  bright  lines  produced  by  the  gas  or  vapor 
alone,  ichen  incandescent.  In  other  words,  the  vapor  or 
gas  through  which  the  light  is  transmitted,  absorbs  or 
extinguishes  exactly  those  rays  which  it  is  capable  itself 
of  emitting.  If  the  vapor  alone  would  produce  a  yellow 
line,  the  vapor  transmitting  light  from  an  incandescent 
solid  or  liquid  produces  a  dark  line  in  the  place  of  the 
yellow.  If  incandescent  hydrogen  produce  a  bright  line 
in  the  orange,  an  atmosphere  of  hydrogen  transmitting 
light  from  a  solid  or  liquid  body  will  produce  a  dark  line 
in  exactly  the  same  part  of  the  orange.* 

*For  a  full  exposition  of  the  principles,  methods  and  results  of  spectral 
analysis,  seeSchellen:  Spectralanalyse,  translated  and  republished  in  America 
as  Spectrum  Analysis  in  its  Application  to  Terrestrial  Substances  and  the  Phys- 


40  COSMICAL    DUST. 


SYNOPTICAL   VIEW   OF   SPECTROSCOPIC    PRINCIPLES. 
DESIGNATION   OF   SPECTRUM.  CONDITION   OP   MATTER. 

Continuous  Spectrum  [      j  Incandescent    Solid    or    Liquid 

(Drummond  Light). 

Bright-line  Spectrum  =          1        f 

Discontinuous  Spectrum=  I  .     ^^^  Gas  or  Vapor  (Elec- 
Direct  Spectrum=  \  I  \      <™  Lf^}  S^r  f  eminences; 

Gas  Spectrum  \\[     Irresolvable  Nebula). 

Dark-line  Spectrum  =  "1  "  f  Incandescent    Solid    or    Liquid 

Absorption  Spectrum,  shining  through  gas  or  vapor 

Reversed  *  Spectrum  or       f      j      of    lower    temperature    (Sun  ; 
Compound  Spectrum          J       [     Fixed  Siars). 

When  these  principles  are  applied  to  the  investigation 
of  cosmical  light,  they  reveal  the  physical  conditions  of 
the  matter  which  emits  it.  For  instance,  the  light  of  the 
moon  gives  the  same  spectrum  as  direct  sunlight.  The 
same  is  true  of  the  light  reflected  from  the  planets.  This, 
of  course,  confirms  the  astronomical  doctrine  that  the 
planets  and  satellites  shine  only  by  reflected  light.  If  we 
investigate  the  light  emitted  by  the  tail  or  the  coma  of  a 
comet,  we  find  that  also  to  give  the  same  spectrum  as 
sun-light.  Hence  the  tail  and  coma  of  a  comet  are  not 
self-luminous.  The  nucleus  of  the  comet,  however,  gives 
a  spectrum  of  three  bright  lines.  This  demonstrates,  first, 
that  the  nucleus  is  an  incandescent  gas  or  vapor;  and  sec- 
ondly, that  it  contains  carbon,  since  the  bright  lines  corre- 
spond to  the  spectrum  of  a  compound  of  carbon. 

If  now,  we  turn  the  spectroscope   to  the  nebulae,  we 

leal  Constitution  of  the  Heavenly  Bodies,  1872.  Also  in  abbreviated  form, 
Half  -Hour  liecreations  in  Science,  Nos.  3  and  4,  Boston  ;  also  Roscoe  :  S/>ectrum 
Analysis,  Lond.,  2d  ed.,  1870,  8vo.  pp.  404.  The  reader  will  find  important  anil 
beautiful  applications  of  the  spectroscope  in  Secchi:  Le  Soleil,  2  vols.  and 
Atlas;  and  Young:  The  Sun,  New  York,  1881. 

•Quite  commonly  now,  the  term  "reversed"  is  applied  to  bright  lines 
appearing,  particularly  in  solar  spectra,  in  the  places  where  dark  lines  usually 
appear,  as,  for  instance,  in  the  lines  due  to  the  deepest  part  of  the  solar  spots, 
and  in  the  protuberances.  See  Yonng:  The  Sun,  130,  157,  which  compare  with 
pages  83  and  84.  See  also  Secchi  :  Le  Soleil,  i,  283-4  ;  ii,  83-98,  etc. 


NEBULA.  41 

discover  that  almost  all  those  nebulae  which  have  been 
resolved  give  spectra  identical  with  the  spectra  of  the  sun 
and  the  ordinary  fixed  stars.*  This  is  a  grand  consumma- 
tion. It  shows  that  the  resolvable  nebulae  are  possibly 
what  Sir  William  Herschel  conceived  them  —  vast  firma- 
ments of  suns  analogous  to  that  firmament  in  which  our 
sun  is  a  star.  We  might  picture  to  ourselves,  on  the 
basis  of  this  conception,  thousands  upon  thousands  of 
other  firmaments,  each  with  its  milky  way,  its  constella- 
tions, its  variable  stars,  its  countless  dark,  unseen,  but 
probably  habitable  planets  floating  away  in  immensity, 
each  with  its  peculiar  domestic  economy,  and  each,  never- 
theless, under  the  common  government  of  a  single  empire 
whose  ministers  are  gravitation,  heat,  light,  ether.  At- 
tempting to  grasp  the  conception  in  its  magnitude,  we 
feel  ourselves  lifted  into  another  realm  of  being.  The 
limitations  of  earth  and  material  existence  are  left  be- 
hind, and  we  dwell,  gifted  with  a  sort  of  omnipresence, 
in  the  immensity  of  God's  universe. 

But  what  of  the  irresolvable  nebulae?  Their  spectra 
yield  only  bright  lines.  Similar  as  they  are  in  general 
aspect,  to  the  resolvable  nebulae,  their  spectra  are  funda- 
mentally different.  Their  physical  condition,  accordingly, 
is  that  of  a  glowing  gas  or  vapor.  They  are  not  firma- 
ments of  suns.  They  are  incandescent  cosmical  dust. 
They  are  dust  so  intensely  heated  that  some  or  all  of  it  is 
in  a  state  of  vaporization.  This  is  another  grand  consum- 
mation. A  matured  conjecture  of  Sir  William  Herschel 
is  confirmed.  The  world-stuff  which  Laplace  demanded  is 
at  hand.  Let  us  see  whether  the  aspects  which  it  presents 
sustain  the  idea  of  progressive  world-growth. 

Evidences  of  development  seem  to  be  afforded  by  the 
forms  of  the  nebulae.  Of  these  we  may  enumerate  the 
following  classes  : 

*It  is  impossible  to  say  whether  the  apparently  continuous  spectra  of  some 
of  these  nebulae  are  crossed  or  not  by  dark  lines. 


42  COSMICAL    DUST. 

1.  Amorphous  Nebulce. —  Here  we  may  include  the 
great  nebula  in  the  sword-handle  of  Orion.*  I  reproduce 
for  the  reader  (Figure  6)  the  careful  drawing  executed  by 
Trouvelot.f  This  is  one  of  the  brightest  of  the  nebulae; 
but  at  the  same  time  it  has  resisted  all  efforts  at  resolu- 
tion. Its  spectrum,  accordingly,  consists  of  a  small  num- 


FIQ.  6.    THE  GREAT  NEBULA  IN  ORION.    CENTRAL   PAI 
TROUVELOT. 


DRAWN  BY    L. 


ber  of  bright  lines.  Here  belong  also,  the  two  Magellanic 
Clouds,  visible  to  the  naked  eye  in  the  southern  hemi- 
sphere. I  am  not  aware  that  their  spectrum  has  been 
obtained. 

2.    Spiral   tfebulce.—The    nebula    No.    3,239    Herschel 

*  Director  Otto  Strnve  classes  this  among  spiral  nebula:  (Monthly  Notices, 
Astronomical  Society,  London,  14  March,  1856,  xvi,  139;  Gautier,  Archives  des 
Sciences  Physiques  et  Naturelles,  Geneva,  1862,  translated,  Smithsonian  Report, 
1863,299).  It  is  possibly  beginning  to  pas*  into  the  spiral  phase.  See  also  Prof. 
Geo.  Bond:  On  the  Spiral  Structure  of  the  great  Nebula  In  Orion,  Monthly  No- 
tices, xxii,  203-7. 

t  Further,  on  this  nebula,  see  Nature,  22  November,  1877,  p.  67,  and  18  July, 
1878,  p.  313;  Schellen:  Spectral  Analysis,  534. 


NEBULA.  43 

(Figure  7)  presents  the  form  of  a  sickle  or  greatly  curved 
tail  of  a  comet.  It  seems  to  be  an  elongated  mass  of  light 
just  beginning  a  gyration  about  a  centre  a  little  to  one 
side  of  the  head.  A  remarkable  spiral  nebula  is  Herschel 
1,173.*  But  the  most  striking  of  all  spiral  nebulas  is  that 
situated  in  Canes  Venatici  (H.  1,622;  Figure  8).  It  is 


FIG.  7.  SICKLE-SHAPED  NEBULA,  HEHSCHEL  3,239. 

impossible  to  gaze  upon  these  figures  without  feeling 
the  conviction  that  a  spiral  movement  is  in  progress.  The 
spectra  of  these  nebulae  have  not  been  certainly  ascer- 
tained ;  but  we  may  venture  the  conjecture  that  they  will 
be  found  to  consist  of  bright  lines.  Such  a  spectrum,  at 
least,  is  given  by  the  spiral  nebula  H.  4,964,  in  which  lines 

*See  view  in  Schellen,  op.  cit.,  538. 


44  COSMICAL    DUST. 

answering  to  nitrogen  and  hydrogen    appear,  besides  two 
other  bright  lines  not  identified. 


FIG.  8.  SPIRAL  NEBULA  IN  CANES  VENATICI,  HERSCHEI.  1. 

3.    Spiro-annular  Nebula. — These  seem  to  be  undergo- 
ing a  transition  from  the  spiral  to  the  annular  form.    H.  604 

(Figure  9)  is  one  of 
these.  Another  equal- 
ly transitional  is  H. 
854  (Figure  10),  in 
which  we  see  several 
segments  of  spiral  or 
annular  forms  sur- 
rounding a  bright  nu- 
cleus, as  in  H.  604. 
The  spectra  of  these 
nebulae  are  also  un- 

Fio.9.  SPIRO-AXNULAR  NEBULA,  HERSCHEL  604.    known.* 

*  This,  like  most  of  the  other  nebular  types  mentioned  may  be  found  well 
figured  in  Schellen's   Spectral  Analysis,  and  better  in    The  Popular  Science 


NEBULA. 


.Fia.  10.  SPIBO-ANNULAR  NEBULA,  HERSCHEL  854.    INDICATIONS  or  SEVERAL 
RINGS. 

4.  Annular  Nebulce, — A  fine  example  of  this  form  is 
the  annular  nebula  in  the  Lyre,  H.  4,457  (Figure  11).  Its 
spectrum  consists  of  one  bright  line  answering  to  nitrogen. 
The  annular  nebula  is  sometimes  presented  obliquely  to 
view,  as  in  H.  1,909.  Sometimes  it  appears  edgewise,  as 
in  H.  2,621.  At  other  times  it  is  so  attenuated  at  oppo- 
site sides  as  to  be  invisible  in  those  places,  and  appears, 
accordingly,  as  a  double  nebula,  as  in  H.  3,501  and  H. 
2,552.  More  powerful  instruments  may  be  expected  to 
show  the  ring  complete.  In  both  these  cases  there  is  a 
central  mass  more  or  less  luminous,  as  in  H.  854,  H.  604 
and  H.  4,447.  The  nebula,  Figure  10,  seems  likely  to 

Monthly  for  June,  1873.  Newcomb's  Popular  Astronomy  also  gives  views  of 
The  Great  Nebula  in  Orion,  the  Annular  Nebula  in  the  Lyre,  the  Omega  Nebula 
H.  2,008,  the  Nebula  H.  3,722,  and  the  Looped  Nebula  H.  2,941.  But  the  most 
exquisitely  delicate  representations  of  nebula;  are  found  on  two  plates  of  Secchi : 
Le  Soleil,  vol.  ii. 


4G 


COSMICAL    DUST. 


FIG.  11.  ANNULAR  NEBU 

FROM  A  DRAWING  BY  PROF.  HOLDEN. 


consist  of  a  central  mass 
surrounded  by  several 
rings  which  may  be 
hereafter  more  distinct- 
ly discerned. 

5.  Planetary  Nebulae. 
— These  are  nebulae  with 
tolerably  definite  circu- 
lar outlines,  and  consist 
either  of  a  uniform  disc, 
as  defined  by  Herschel, 
or  of  a  rudely  annular 
or  spiral  belt  surround- 

ing   a    faint   luminosity, 
THE  LYRE.  J) 

which  often  contains  one 

or    more    bright    nuclei. 

The  bright  belt  is  often  fringed  by  a  coma  or  a  bur  of 
light.  H.  2,241,  as  shown  in  Figure  12,  consists  of  a  well 
defined  belt  of  light  surrounded 
by  an  irregular  coma,  but  without 
a  nucleus.  H.  464  shows  a  bright 
ring  of  the  spiral  order.  It  is 
surrounded  by  a  bur  of  light, 
and  has  two  nuclei  which  scarce- 
ly sustain  any  relations  to  the 
general  structure.  H.  838,  Fig- 
ure 13,  has  a  ring  of  light  consist- 
ing of  a  double  band  of  the  spiral 
order.  It  is  surrounded  by  a  bur 
of  light,  and  contains  two  nuclei 

symmetrically  situated,  and  surrounded  each  by  a  dark 
zone,  a  luminous  haze  and  a  bright  ring.  The  planetary 
nebula  in  Aquarius  (H.  2,098),  consists  of  a  sphere  of 
luminosity  surrounded  by  a  fringe  of  rays.  From  each 
side  of  the  sphere  projects  a  protuberance  equal  in  length 


FIG.  12. 

PLANETARY  NEBULA,  H.  2,241 
WITHOUT  A  NUCLEUS. 


NEBULAE. 


47 


FIG.  13. 

PLANETARY  NEBULA,  H. 
WITH  TWO  NUCLEI. 


to  the  radius  of  the  sphere. 
This  phenomenon,  it  has 
been  suggested,  may  result 
from  edgewise  presentation 
of  a  ring.  This  nebula  gives 
a  spectrum  of  three  bright 
lines,  one  of  which  is  due  to 
hydrogen  and  one  to  nitro- 
gen. 

6.  Stellar  Nebulae.— These 
consist  of  a  bright  nucleus 
more  or  less  resembling  a 
star,  which  is  surrounded  by 
a  disc  of  light,  sometimes  in  alternating  bands  of  bright- 
ness. The  nebula  H.  450  is  one  of  this  class,  very  strongly 
marked,  and  it  has  a  spectrum  of  three  bright  lines.  One 
cannot  help  remarking  the  resemblance  to  a  stellar  nebula 
presented  by  Donati's  comet,  on  the  second  of  June,  1858. 
When  the  central  body  is  sharply  defined  like  a  star,  the 
object  is  known  as  a  "nebulous  star." 

The  six  foregoing  classes  of  nebulae  all  give,  so  far  as 
ascertained,  spectra  of  bright  lines.  They  are,  therefore, 
masses  of  glowing  gas.  About  sixty  nebulas  have  been 
investigated  by  Huggins  spectroscopically,  with  results 
which  are  satisfactory  for  the  present.  A  much  larger 
number  were  found  too  faint  to  yield  results  which  could 
be  relied  upon.  Of  the  sixty,  about  one-third  yield 
spectra  of  bright  lines,  and  about  two-thirds  yield  spectra 
apparently  continuous.  It  is  an  interesting  fact  that  all 
nebulas  giving  bright-line  spectra  remain  completely  irre- 
solvable; and  all  nebulae  which  are  resolvable  give  continu- 
ous spectra.  The  "resolvable  nebulas,"  therefore,  do  not 
constitute  a  class  of  proper  nebulae.  More  than  half  of 
those  forms  once  regarded  as  nebulae  must  be  set  down  as 


48  COSMICAL    DUST. 

starry  clusters.*     But  at  least  one-third  of    all  so-called 
nebulae  are  real  nebulas — masses  of  incandescent  vapor. 

§  6.   UNIVERSAL  WORLD-STUFF. 

1.  Cosmical  Dust, — The  cosmical  realm  appears,  from 
the  survey  which  we  have  taken,  to  be  abundantly  stocked 
with  the  crude  material  of  which  worlds  are  formed.  The 
most  familiar  substances  of  our  earth  are  found  in  meteor- 
ites, comets,  and  irresolvable  nebulas,  as  well  as  in  resolv- 
able nebulas,  stars  and  suns.  But  one  system  of  matter 
pervades  the  immense  spaces  of  the  visible  universe;  and 
it  is  a  dream  of  physical  philosophy  that  all  the  recognized 
chemical  elements  will  one  day  be  found  but  modifications 
of  a  single  material  element,  f  When  this  dream  is  real- 

*  Prof.  Newcomb,  Popular  Astronomy,  p.  444,  has  given  views  of  two  such 
"clusters." 

t  It  is  generally  admitted  that  at  excessively  high  temperatures,  matter 
exists  in  a  state  of  dissociation — that  is,  no  chemical  combination  can  exist. 
Now,  if  the  eo-called  elements  are  really  compounded,  a  state  of  dissociation 
would  resolve  them  into  ultimate  atoms  or  molecules,  all  of  one  kind.  The 
spectrum  of  such  a  substance  should  be  a  bright  line.  If  the  temperature  is 
such  that  two  or  three  different  molecular  arrangements  may  exist,  the  spectrum 
should  consist  of  two  or  three  bright  lines.  The  question  may  reasonably  be 
raised  whether  the  nebulae  which  give  two  or  three  bright  lines  are  in  such  a 
condition.  Dumas,  in  1857,  based  the  suggestion  of  the  composite  nature  of  the 
"  elements"  on  certain  relations  of  atomic  weights.  (See  also  Oomptes  Rendus, 
Nov.  3,  1873'.)  The  conception  was  maintained  in  1866,  and  subsequently,  by 
Professor  G.  Hinrichs  (Atomechanik;  also  Amer.  Jour.  Set.,  II,  xxx,  19,  56,  id. 
Ill,  i,  319),  from  a  consideration  of  the  physical  properties  of  the  atoms;  and 
further,  in  1874,  from  the  relations  of  atomicity  and  atomic  weights  (G.  Hin- 
richt»:  The  Principles  of  Chemistry  and  Molecular  Mechanics,  182.  See  also, 
Atner.  Jour.  Set.,  II,  xxxii,  350,  and  Proc.  Amer.  Atsoc.,  1869,  112).  Berthelot 
maintains  that  the  atoms  of  the  elements  are  composed  of  the  same  matter,  dis- 
tinguished only  by  the  motions  set  up  in  them ;  and  accordingly  II.  Ste.  Claire 
Deville  affirms  that  "  when  bodies  deemed  to  be  simple  combine  with  one 
another,  they  vanish,  they  are  individually  annihilated."  Dr.  E.  Haanel  has 
clearly  shown  that  the  phenomena  of  allotropism  and  combining  proportions 
demand  the  admission  of  the  complex  constitution  of  the  elements  (address 
before  the  Ontario  Association  for  the  Advancement  of  Education,  1876).  Pro- 
fessor Lockyer  has  published  some  strikingly  confirmatory  conclusions  based  on 
spectroscopic  phenomena  (J.  N.  Lockyer:  Discussion  of  the  Working  Hypoth- 
esis that  the  So-called  Elements  are  Compound  Bodies,  Proc.  Roy.  Soc.,  xxviii, 
159,  12  Dec.,  1878;  Comptes  Bendus,  Nov.,  1878;  Amer.  Jour.  Sci.,  Ill,  xvii,  64, 


WORLD-STUFF.  49 

ized,  we  shall  behold  the  amazing  phenomenon  of  a 
universe  with  its  numberless  forms,  conditions  and  aspects 
built  out  of  a  single  substance. 

2.  Elemental  Atoms, — The  conception  of  matter  of 
some  sort  existing  in  a  highly  attenuated  state  throughout 
the  remote  regions  of  space  appears  to  be  as  old  as  the 
age  of  Newton.  Indeed,  the  doctrine  of  the  universal 
diffusion  of  material  stuff  in  a  chaotic  period,  before  the 
organization  of  the  universe,  was  a  central  conception  of 
the  Greek  atomists,  as  well  as  of  all  those  physical  specu- 
lators who  maintained  the  theory  of  a  plenum,  down  to 
Descartes.*  The  doctrine  of  attenuated  matter  diffused 
through  the  intercosmical  spaces  of  organized  systems  is 
distinct.  Dr.  T.  S.  Hunt  has  called  attentionf  to  some 

93-116;  Nature,  xxi,  5;  xxii,  4-7,  xxiv,  3%,  Aug.  25,  1881.  Necessity  for  a  New 
Departure  in  Spectrum  Analysis  (Nature,  Nov.  6, 1879,  Comptes  Rendus,  xcii,  904). 
But  see  criticisms  on  Lockyer's  views  by  H.  W.  Vogel,  Monatsber.  der  Berliner 
Akad.  der  Wiss.,  1880, 192  and  Nov.  2,  1882,  Nature,  xxvii,  2*3;  also  by  Liveing 
and  Dewar,  Proc.  Roy.  Soc.,  30,  93 ;  Wied.  Beibl.  iv,  366.  See  also  results  attained 
by  A.  Schuster,  Nature,  xxii,  444,  Prof.  F.  W.  Clarke  entertains  kindred  views 
(Pop.  Sci.  Monthly,  ii,  32,  Jan.  1873;  Science  News,  Feb.  15,  1879,  114).  Dr.  J.  G. 
Macvicar  has  also  speculated  on  the  assumed  identity  of  the  ultimate  elements, 
and  their  common  constitution  with  the  ethereal  fluid  (A  Sketch  of  a  Philosophy, 
Parts  I  and  II,  London,  1868) ;  while  the  late  remarkable  experiments  of  Dr. 
Crooks  on  so-called  "  radiant  matter"  (W.  C.  Crooks,  Nature,  xxii,  101-4,  125-8, 
153-4,  Amer.  Jour.  Sci.  Ill,  xvii,  281;  xviii,  241-62;  Pop.  Science  Monthly,  xvi, 
13-24,  157-67),  would  seem  to  be  best  understood  on  the  hypothesis  of  the  homo- 
geneity of  the  elements  of  matter,  and  the  continuity  of  the  states  of  matter. 
The  ethereal  ground  of  all  matter  is  also  maintained  by  M.  Moigno  (Acad.  des 
Sci.,  April  16,  1883,  and  by  Prof.  Oliver  Lodge  (Nature,  xxvii,  304-6,  328-30,  par- 
ticularly p.  330),  whose  position  is  criticised  by  S.  Tolver  Preston  (Nature,  xxvii, 
579).  See  also  Newton's  suggestions  given  below.  The  final  demonstration 
seems,  therefore,  to  be  impending,  and  the  dream  of  science  is  promised  a 
fulfilment.  See  further  on  this  subject  the  suggestive  lecture  of  Sir  Benjamin 
Brodie  on  Ideal  Chemistry,  1867,  reprinted  1880,  as  also  a  very  accessible  paper 
by  Professor  F.  W.  Clarke  in  Popular  Science  Monthly,  No.  xlvi,  Feb.  1876, 
463-71;  but  more  particularly  in  reference  to  the  cosmical  diffusion  of  disso- 
ciated matter,  see  beyond  with  the  appended  references. 

*  See  Part  iv  of  this  work. 

tHunt:    Celestial   Chemistry  from  the  Time  of  Newton,  read  before  the 
Cambridge  Philosophical  Society,  Nov.  28.  1881,  reprinted  from  its  Proceedings, 
Amer.  Jour.  Sci.  Ill,  xxiii,  123-33,  Feb.,  1882.     I  have  depended  greatly  on  Dr 
Hunt's  suggestions  in  arranging  the  historical  memoranda  which  follow. 
4 


50  COSMICAL    DUST. 

long-neglected  passages  in  Newton's  works,  from  which  it 
appears  that  a  belief  in  such  universal,  intercosmical 
medium  gradually  took  root  in  his  mind.  Newton,  as  his 
well  known  letter  to  Bentley  proves,  was  persuaded  that 
the  power  of  attraction  could  not  be  exerted  by  matter 
across  a  vacuum.  These  passages  show  what  were  his 
views  respecting  the  nature  of  the  interplanetary  medium 
of  communication.  Though  declaring  that  "  the  heavens 
are  void  of  all  sensible  matter,"  he  elsewhere  exceptecl 
"perhaps  some  very  thin  vapors,  steams  and  effluvia,  aris- 
ing from  the  atmospheres  of  the  earth,  planets  and  comets, 
and  from  such  an  exceedingly  rare  ethereal  medium  as  we 
have  elsewhere  described."*  The  "ethereal  medium" 
referred  to  here  had  been  suggested  in  his  "Hypothesis," 
of  1675,  where  he  imagines  "an  ethereal  medium  much  of 
the  same  constitution  with  air,  but  far  rarer,  subtler  and 
more  elastic."  "But  it  is  not  to  be  supposed  that  this 
medium  is  one  uniform  matter,  but  composed  partly  of 
the  main  phlegmatic  body  of  ether,  partly  of  other  various 
ethereal  spirits,  much  after  the  manner  that  air  is  com- 
pounded of  the  phlegmatic  body  of  air  intermixed  with 
various  vapors  and  exhalations."  He  conceives  this  me- 
dium to  be  in  continual  movement  and  interchange.  "For 
nature  is  a  perpetual  circulatory  worker,  generating  fluids 
out  of  solids,  fixed  things  out  of  volatile,  and  volatile  out 
of  fixed;  subtile  out  of  gross,  and  gross  out  of  subtile; 
some  things  to  ascend  and  make  the  upper  terrestrial 
juices,  rivers  and  the  atmosphere,  and  by  consequence, 
others  to  descend  for  a  requital  to  the  former.  And  as 
the  earth,  so  perhaps  may  the  sun  imbibe  this  spirit  copi- 
ously to  conserve  his  shining  and  keep  the  planets  from 
receding  further  from  him;  and  they  that  will  may  also 
suppose  that  this  spirit  affords  or  carries  with  it  thither 

*  Newton:  Optics,  Bk.  III.  Query  28, 1704. 


WORLD-STUFF.  51 

the  solary  fuel  and  material  principle  of  life,  and  that  the 
vast  ethereal  spaces  between  us  and  the  stars  are  for  a 
sufficient  repository  for  this  food  of  the  sun  and  planets." 
Then  rising  to  a  still  higher  generalization,  he  adds: 
"  Perhaps  the  whole  frame  of  nature  may  be  nothing  but 
various  contextures  of  some  certain  ethereal  spirits  or 
vapors,  condensed,  as  it  were,  by  precipitation,  much  after 
the  same  manner  that  vapors  are  condensed  into  water  or 
exhalations  into  grosser  substances,  though  not  so  easily 
condensable,  and  after  condensation  wrought  into  various 
forms;  at  first  by  the  immediate  hand  of  the  Creator,  and 
ever  since  by  the  power  of  nature,  which,  by  virtue  of  the 
command  'increase  and  multiply,'  became  a  complete  imi- 
tator of  the  copy  set  her  by  the  great  Protoplast.  Thus, 
perhaps,  may  all  things  be  originated  from  ether." 

Twelve  years  later*  Newton  strengthened  this  hypothe- 
sis by  additional  considerations.  The  tails  of  comets 
were  conceived  to  afford  exhalations  which,  with  progres- 
sive rarefaction  and  dilatation,  spread  throughout  space, 
and  being  thus  brought  under  the  attraction  of  the  planets, 
mingle  with  their  atmospheres  and  contribute  support 
for  vegetable  life.  But  since  vegetation  when  decaying 
passes  in  part  into  solid  states,  while  fluids  are  demanded 
for  the  continued  sustenance  of  the  vegetable  kingdom, 
the  continued  supply  of  these  fluids  must  come  from  some 
external  source.  This  supply,  he  thought,  might  originate 
chiefly  in  the  tails  of  comets. 

Still  later  f  he  conceived  that  similar  exhalations  might 
proceed  from  other  celestial  bodies,  for  he  speaks  of  the 
sun  and  fixed  stars  as  great  earths,  intensely  heated  and 
surrounded  with  dense  atmospheres  which,  by  their  weight, 
condense  the  exhalations  arising  from  these  hot  bodies. 
In  succeeding  editions  he  develops  the  idea  of  exhalations 

*  Prmcipia,  Bk.  Ill,  prop.  41,  1st.  ed.  1687. 
t Newton:   Optics,  1st.  ed.,  1704,  Query  U, 


52  COSMIC  A  L    DUST. 

or  vapors  proceeding  from  the  sun  and  other  heavenly 
bodies,  and  by  expansion  "through  all  the  heavens,"  con- 
stituting a  medium  universally  diffused.  This  theory  con- 
tinued to  take  more  definite  shape  in  the  mind  of  Newton 
till,  in  the  latest  editions  of  the  Principia  and  Optics, 
he  enunciates  the  clear  conception  of  a  thin  interstellary 
matter  "arising  from  the  sun,  the  fixed  stars  and  the  tails 
of  comets,  and  falling  by  gravity  into  the  atmospheres  of 
the  planets,  there  becoming  condensed  and  passing  gradu- 
ally, through  the  influence  of  gentle  heat,  into  the  form 
of  salts,  sulphurs  (that  is,  combustible  matters),  tinc- 
tures, slime,  mud,  clav,  sandstones,  coral  and  other  terres- 
trial substances."* 

The  notion  of  the  existence  of  a  subtile  ethereal  medium, 
suggested,  as  is  thought,  by  passages  in  the  works  of  Sir 
Isaac  Newton,  maintained  a  place,  in  scientific  and  philo- 
sophic speculations,!  but  the  somewhat  different  notion 
of  a  diffused  matter  not  differing  in  its  substance  from 
ordinary  matter,  met  with  almost  no  response  until  1842, 
when  Professor  \V.  R.  Grove,  in  a  lecture  at  the  London 
Institution,  propounded  the  theory  that  heat  and  light  are 
affections  "of  matter  itself,  and  not  of  a  distinct  ethereal 
fluid  permeating  it;  "  and  he  added:  "  With  regard  to  the 
planetary  spaces,  the  diminishing  periods  of  comets  is  a 
strong  argument  for  the  existence  of  a  universally  dif- 
fused matter;  this  has  the  function  of  resistance,  and 
there  appears  to  be  no  reason  to  divest  it  of  the  /'unctions 
common  to  all  matter."].  In  his  essay  on  the  Correlation 
of  the  Physical  Forces,  published  in  1843,  he  suggested 

*  Newton:  Principia,  lib.  Ill,  prop.  xlii. 

tSee  especially  Cotnte:  Philosoptiie  Positive;  Ilelmholtz:  Interaction  of 
'tie  Natural  Force*;  Sir  William  Thomson  :  Density  of  (lie  Luminiferous  Ether, 
Tranx.  Roy.  Soc.,  Edinb.,  xxi,  Pt.  i,  1854,  Phil.  Mag.  ix,  36,  1855. 

t  Grovo:  Correlation  of  the  Physical  Forces.  Youmans'  ed..  Preface,  6  and 
7,  The  author  subsequently  states  (p.  123)  that  "the  celebrated  Leonard  Euler 
had  published  a  somewhat  similar  theory." 


WORLD-STUFF.  53 

that  "worlds  or  systems"  "are  gradually  changing  by 
atmospheric  additions  or  subtractions,  or  by  accretions  or 
diminutions  arising  from  nebulous  substance,  or  from 
meteoric  bodies"  (p.  81).  His  whole  essay  is  grounded  on 
the  general  doctrine  that  the  so-called  "imponderable" 
agents  are  nothing  but  "modes  of  motion"  in  ordinary 
matter  excessively  attenuated  and  universally  diffused.* 
In  a  later  edition  he  suggests  that  the  planetary  and 
stellar  atmospheres,  expanded  through  space,  are  probably 
in  "«  state  of  equilibrium  with  reference  to  each  other," 
and  may  "furnish  matter  for  the  transmission  of  the 
modes  of  motion,  which  we  call  light,  heat,". etc.  In  1866 
he  still  further  suggested  f  that  this  diffused  matter  may 
become  a  source  of  solar  heat,  "inasmuch  as  the  sun  may 
condense  gaseous  matter  as  it  travels  in  space,  and  so  heat 
may  be  produced.' 

Almost  simultaneously  with  Grove,  Humboldt  J  placed 
on  record  his  belief  that  "  exact  and  corresponding  obser- 
vations indicate  the  existence  and  the  general  distribution 
of  an  apparently  non-luminous,  infinitely  divided  matter." 
*  *  *  "Of  this  impending  ethereal  and  cosrnical  matter 
it  may  be  supposed  that  it  is  in  motion ;  that  it  gravi- 
tates, notwithstanding  its  original  tenuity;  that  it  is  con- 
densed in  the  vicinity  of  the  great  mass  of  the  sun;  and 
finally,  that  it  may,  for  myriads  of  ages,  have  been  aug- 
mented by  the  vapor  emanating  from  the  tails  of  comets." 
It  is  not  clear  from  Humboldt's  language  that  he  enter- 
tained a  conception  of  diffused  common  matter,  or  only  of 
a  peculiar  fluid,  like  that  insisted  on  by  Dr.  Young.  What 
he  says  is  in  connection  with  the  assumed  ethereal  resist- 

*See,  for  instance,  pp.  81,  123,  138,  139,  151,  187,  198. 

t  Address  as  President  of  the  British  Association,  1866. 

%  Humboldt:  A'osmos,  Otte  translation,  Harpers'  ed.,  i,  86.  The  author  tells 
us  in  his  preface  that  the  work  was  written  for  the  first  time  in  the  years  1843 
and  1844.  though  he  had  "for  many  mouths"  previously  delivered  lectures  on 
the  themes  embraced,  in  Paris  and  Berlin. 


54  COSMICAL   DUST. 

ance  to  the  motion  of  Encke's  comet;  and,  in  another  pas- 
sage, speaking  of  "the  vaporous  matter  of  the  immeasur- 
able regions  of  space,"  he  adds,  "  whether  scattered  with- 
out definite  form  and  limits,  it  exists  as  a  cosmical  ether, 
or  is  condensed  into  nebulous  spots."  His  interchanges  of 
terms,  however,  are  similar  to  those  employed  by  Newton, 
and  it  is  probable  that  Humboldt  did  not  imagine  any 
"cosmical  ether"  having  an  essential  constitution  differ- 
ent from  that  of  ordinary  matter. 

Sir  William  Thompson  in  1854,*  in  a  note  on  the  pos- 
sible density  of  the  luminiferous  ether,  expresses  the  opin- 
ion that  this  substance  is  "  most  probably  a  continuation 
of  our  own  atmosphere."  Sir  Benjamin  Brodie,  on  the 
3d  of  May,  1866,f  read  a  memoir  in  which  he  advanced 
the  idea  that  many  ultimate  chemical  elements  now  only 
known  in  combination  "  may  sometimes  become,  or  may  in 
the  past  have  been,  isolated  and  independent  existences". 
and  on  the  6th  of  June  of  the  following  year  he  pursued 
the  thought  further,:):  advancing  the  suggestion  that  "  in 
remote  ages,  the  temperature  of  matter  was  much  higher 
than  it  is  now,  and  that  these  other  things  (the  ideal  ele- 
ments) existed  in  a  state  of  perfect  gas  —  separate  exist- 
ences —  uncombined." 

But  quite  independently,  arid  a  few  days  earlier  than  Dr. 
Brodie's  last  mentioned  utterance,  very  similar  views  were 
set  forth  by  Dr.  T.  S.  Hunt.  In  a  lecture  on  the  Chemistry 
of  the  Primeval  JEarth,§  he  advanced  the  opinion  that  the 
"breaking  up  of  compounds,  or  dissociation  of  elements,  by 
intense  heat,  is  a  principle  of  universal  application,  so  that 

*  Thomson,  Trans.  Hoy.  Soc.  Edinb.,  xxi,  pt.  i ;  Phil.  Mag.,  ix,  36,  1855. 

+  Brodie:  Calculus  of  Chemical  Operations,  Proc.  Royal  Soc.,  May  3,  1866, 
Phil.  Trans.,  1866. 

;  Brodie:  Ideal  Chemistry,  a  lecture  before  the  Chemical  Society  of  London, 
June  6, 1867,  published  in  the  Chemical  News,  June  14,  1867;  republished  1880, 
in  separate  form,  with  a  preface. 

$  Delivered  before  the  Royal  Institution,  May  31,  1867,  and  published  in  the 
Chemical  News  of  June  21, 1867,  and  in  the  Proceedings  of  the  Royal  Institution. 


WORLD-STUFF.  55 

we  may  suppose  that  all  the  elements  which  make  up  the 
sun,  or  our  planet,  would  when  so  intensely  heated  as  to 
be  in  the  gaseous  condition  which  all  matter  is  capable 
of  assuming,  remain  uncombined;  that  is  to  say,  would 
exist  together  in  the  state  of  chemical  elements;  whose  fur- 
ther dissociation  in  stellar  or  nebulous  masses  may  even 
give  us  evidence  of  matter  still  more  elemental  than  that 
revealed  in  the  experiments  of  the  laboratory,  where  we 
can  only  conjecture  the  compound  nature  of  many  of  the 
so-called  elementary  substances."  Seven  years  later, 
Dr.  Hunt  *  repeated  the  expression  of  these  views,  and 
added  the  hypothesis  suggested  by  Sir  William  Thomson, 
that  our  atmosphere  and  ocean  are  but  portions  of  the  uni- 
versal medium  which,  in  an  attenuated  form,  fills  the 
interstellary  spaces;  and  added  further,  that  "these  same 
nebulas  and  their  resulting  worlds  may  be  evolved  by  a  pro- 
cess of  chemical  condensation  from  the  universal  atmos- 
-phere,  to  which  they  would  sustain  a  relation  somewhat 
analogous  to  that  of  clouds  and  rain  to  the  aqueous 
vapor  around  us."f 

Similar  views,  in  apparent  unconsciousness  of  their 
suggestion  by  preceding  writers,  were  put  forth  in  1870, 
by  Mr.  W.  Mattieu  Williams,:):  who  conceived,  as  Grove 
had  done  in  1866,  that  the  sun's  heat  is  maintained  by  his 
condensation  of  attenuated  matter  everywhere  encoun- 

*In  an  address  at  the  grave  of  Priestley,  on  A  Centunfs  Progress  in  Theo- 
retical Chemistry,  delivered  at  Northumberland,  Pa.,  July  31,  1874;  American 
Chemist,  v,  46-61 :  Pop.  Sci.  Monthly,  vi,  420. 

t  See  these  views  reiterated  in  Preface  to  his  second  edition  of  Chemical  and 
Geological  Essays,  1878,  pp.  ix-xix ;  again  at  meeting  of  British  Assoc.,  Dublin, 
reported  in  Nature,  xviii,  475,  Aug.  29,  1878;  and  also  before  the  French  Acad- 
emy of  Sciences,  published  in  Comptes  Rendus,  Ixxxvii,  452,  Sep.  23,  1878;  and 
still  further  developed  in  an  essay  on  the  Chemical  and  Geological  Relations  of 
the  Atmosphere,  Amer.  Jour.  Sci.,  Ill,  xix,  349-63,  May,  1880;  and  finally,  in  a 
communication  in  Nature,  xxv,  602-3,  Apr.  27,  1882. 

{Williams:  The  Fuel  of  the  Sun.  A  condensed  statement  of  the  contents 
of  this  work  is  contained  in  Current  Discussions  in  Science  by  the  same  author 
in  "Humboklt  Library,'-  No.  41,  Feb.  1883.  See,  also,  Williams  on  the  Radi- 
ometer and  its  Lessons,  Quar.  Jour.  Science,  Oct.  1876. 


56  COSMICAL   DUST. 

tered  in  his  motion  through  interstellary  space.  This 
matter  is  essentially  the  attenuated  state  of  the  atmos- 
phere surrounding  the  cosmical  bodies.  He  suggested 
that  this  diffused  matter  or  ether  which  is  the  recipient 
of  the  heat  radiations  of  the  universe,  is  thereby  drawn 
into  the  depths  of  the  solar  mass.  Expelling  thence  the 
previously  condensed  and  thermally  exhausted  ether,  it 
becomes  compressed  and  gives  up  its  heat,  to  be  in  turn 
itself  driven  out  in  a  rarefied  and  cooled  state,  and  to  absorb 
a  fresh  supply  of  heat  which  he  supposes  to  be  in  this 
way  taken  up  by  the  ether,  and  again  concentrated  and 
redistributed  by  the  suns  of  the  universe  (chapter  V). 

Mr.  Williams'  suggestion  was  adopted  by  Dr.  P.  Mar- 
tin Duncan  *  who,  in  1877,  also  without  the  knowledge  of 
Grove's  priority,  but  also  rejecting  Williams'  assumption 
of  the  equilibrated  condition  of  the  atmospheres  of  the 
heavenly  bodies,  conceived  the  sun  to  be  slowly  attracting 
to  itself  the  earth's  atmospheric  envelope,  and  proceeds  to 
deduce  from  this  premise  a  secular  diminution  of  the 
earth's  climatic  warmth. f 

There  are  few  investigations  the  history  of  which  better 
illustrates  the  interesting  coincidences  of  conviction  in 
different  minds  working  in  complete  personal  indepen- 
dence of  each  other.  Some  recently  propounded  theory  or 
conjecture,  or  some  scientific  stadium  reached  through  the 
combined  efforts  of  many  investigators,  seems  to  set 
many  intellects  in  a  similar  mood,  in  which,  by  the  laws 
of  thought,  expectation  and  attention  are  turned  in  one 
common  direction,  so  that  some  new  conception  springs 
into  existence  independently  in  many  minds.  This  princi- 
ple is  still  further  exemplified  in  connection  with  the  doc- 

*  In  an  address  as  President  of  the  Geological  Society,  London,  May,  1877. 

tThe  cosmical  bearing  of  the  doctrine  of  dissociation  of  matter  at  high 
temperatures  is  also  impljed  in  the  publications  of  Prof.  F.  W.  Clarke  and  Mr, 
Lockyer.  previously  cited. 


WORLD-STUFF.  57 

trine  of  disseminated  matter  in  the  case  of  a  recent  theory 
which  it  remains  to  present.  Dr.  C.  William  Siemens  in  a 
recent  memoir  of  extraordinary  interest,  On  the  Conserva- 
tion of  Solar  Energy,*  catching  hold  of  the  suggestions 
of  his  predecessors  respecting  an  all-pervading  medium, 
has  followed  Grove  in  seeking  through  its  condensation 
the  source  of  solar  heat,  though  summoning  to  his  aid 
a  mechanism  both  original  and  striking.  He  supposes 
stellar  space  "  to  be  filled  with  highly  rarefied  gaseous 
bodies,  including  hydrogen,  oxygen,  nitrogen,  carbon  and 
their  compounds,  besides  solid  materials  in  the  form  of 
dust.  This  being  the  case,  each  planetary  body  would 
attract  to  itself  an  atmosphere  depending  for  its  density 
upon  its  relative  attractive  importance,  and  it  would  not 
seem  unreasonable  to  suppose  that  the  heavier  and  less 
diffusible  gases  would  form  the  staple  of  these  atmos- 
pheres, that  in  fact,  they  would  consist  mostly  of  nitro- 
gen, oxygen  and  carbonic  anhydride,  whilst  hydrogen  and 
its  compounds  would  predominate  in  space.f  But  the 
planetary  system  as  a  whole  would  exercise  an  attractive 
influence  upon  the  gaseous  matter  diffused  through  space, 
and  would  therefore  be  surrounded  by  an  interplanetary 

*  Read  at  the  Royal  Society,  London,  March  2,  1883,  and  first  published  in 
Nature,  xxv,  440-4,  March  9,  1883.  See  a  criticism  by  E.  Douglass  Archibald, 
and  Dr.  Siemens'  reply,  in  Nature,  xxv,  504.  See  also  supplementary  views  by 
Charles  Morris  of  Philadelphia  and  Dr.  T.  S.  Hunt  of  Montreal,  together  with 
Dr.  Siemens'  response,  in  Nature,  xxv,  601-3,  April  27,  1882;  also  Prof.  S.  D. 
Liveing's  notice  in  address  as  President  of  the  Chemical  Section,  British 
Association,  Nature  xxvi,  404-5,  August  24,  188J.  This  memoir  was  also  pub- 
lished, with  some  modifications  and  additions,  in  The  Nineteenth  Century,  May 
1883.  The  Popular  Science  Monthly,  June,  1882,  in  Annales  de  Chitnie  et  de 
Physique,  and  other  journals. 

t  On  this  theory  an  atmosphere  ought  to  be  collected  about  the  moon,  of 
one-sixth  the  density  of  the  terrestrial  atmosphere.  That  is,  the  moon  should 
possess  an  atmosphere  capable  of  producing  some  discernible  refraction.  Also 
Jupiter  should  possess  an  atmosphere  more  conspicuous  than  that  of  Mars,  in 
proportion  as  his  effective  surface  attraction  is  greater.  Dr.  T.  S.  Hunt  re- 
minds us  that  according  to  Saemann  the  moon's  atmosphere  has  been  absorbed; 
but  then  we  have  to  inquire  what  has  prevented  renewed  condensation  about 
the  moon?— even  after  all  pores  of  the  moon  have  been  filled. 


58  COSMICAL    DUST 

atmosphere  holding  an  intermediate  position  between  the 
planetary  atmospheres  and  the  extremely  rarefied  stellar 
space." 

This  conception  is  supported  by  the  consequences  of 
the  molecular  theory  of  gases  as  laid  down  by  Clerk  Max- 
well, Clausius  and  Thomson;  since  it  would  be  difficult  to 
assign  a  limit  to  a  gaseous  atmosphere  in  space.  Further, 
it  has  been  directly  asserted  by  various  authors  from  New- 
ton down,  as  I  have  already  shown;  and  Dr.  Flight,  like 
others  before  him,  has  detected  in  meteoric  stones  large 
quantities  of  occluded  carbonic  oxyde,  hydrogen  and  ni- 
trogen, with  smaller  amounts  of  light  carburetted  hydrogen 
or  marsh  gas,  and  carbonic  anhydride  ;  *  all  which  gases 
must  have  been  absorbed  in  distant  space,  as  the  time  of 
flight  through  our  atmosphere  is  too  brief,  and  the  heat 
produced  by  friction  too  great.  Again,  spectrum  analysis 
indicates  the  presence  of  gaseous  matter  in  space;  and 
according  to  the  testimony  of  Dr.  Huggins,  carbon,  hydro- 
gen, nitrogen  and  probably  oxygen  exist  in  cometary 
nuclei,  while,  according  to  the  views  of  Dewar  and  Live- 
ing,  nitrogenous  compounds,  such  as  cyanogen,  are  also 
present.  Dr.  Siemens  thinks  aqueous  vapor  present  in 
space,  though  it  is  not  detected  in  meteoric  stones  in  con- 
sequence of  the  intense  heat  to  which  they  have  been  sub- 
jected. Captain  Abney  found  benzine  and  ethyl  in  the 
atmosphere  at  sea-level,  and  in  equal  quantities  at  the 
altitude  of  8,500  feet.f 

Applying  these  conceptions  to  the  problem  of  solar 
heat,  Dr.  Siemens  holds  that  the  sun  and  planets  commu- 
nicate some  of  their  own  motion  of  rotation  to  the  atmos- 
pheres condensed  about  them,  and  he  supposes  that  in  this 

*The  following  are  the  proportions:  CO*,  0.12;  CO,  31.88;  H,  45.79;  CH4, 
4.55;  N,  17.66;  Total,  100.  Some  meteoric  stones  have  been  found  to  contain 
six  times  their  own  volume  of  these  gases. 

t  Nature,  xxvi,  586. 


WORLD-STUFF.  59 

way  an  action  like  that  of  a  blowing  fan  is  set  up,  by 
which  the  equatorial  part  of  the  sun's  atmosphere  acquires 
such  a  velocity  as  to  stream  out  to  a  distance  beyond  the 
earth's  orbit,  while  an  equal  quantity  of  gas  is  drawn  in 
at  the  poles  to  maintain  equilibrium.  The  gases  thus 
driven  to  a  distance  in  planetary  space  must,  of  course, 
be  enormously  expanded  and  highly  attenuated,  and  in 
this  state  Dr.  Siemens  thinks  that  such  of  them  as  are 
compound  may  be  decomposed  by  absorbing  the  solar 
radiation,  and  thus  the  kinetic  energy  of  solar  radiation 
be  converted  into  the  potential  energy  of  chemical  separa- 
tion. These  dissociated  vapors,  in  consequence  of  the  fan- 
like  action  resulting  from  the  rotation  of  the  sun,  must 
eventually  be  drawn  in  again  at  the  polar  regions.  Here, 
becoming  heated  both  by  increased  density  and  by  solar 
emission,  they  would  burst  into  flame  at  a  point  where 
both  their  density  and  temperature  should  have  reached 
the  necessary  elevation  to  induce  combustion.  The  re- 
sulting aqueous  vapor,  carbonic  anhydride  and  carbonic 
oxide  would  be  drawn  toward  the  equatorial  regions,  and 
be  there  again  projected  into  space  by  centrifugal  force.* 
The  annexed  diagram,  accompanying  Dr.  Siemens' 
memoir,  is  described  by  him  as  "  an  ideal  corona  repre- 
senting an  accumulation  of  igneous  matter  upon  the  solar 
surfaces,  surrounded  by  disturbed  regions  pierced  by  occa- 
sional vortices  and  outbursts  of  metallic  vapors,  and  cul- 
minating in  outward  streams  projecting  from  the  equatorial 
surfaces  into  space  through  many  thousands  of  miles." 
Dr.  Siemens  states  that  an  American  observer  has  informed 

*  The  conditions,  it  will  be  perceived,  are  not  those  of  a  rotating  body  sur- 
rounded by  empty  space.  In  the  latter  case,  the  centrifugal  force  of  the  sun 
would  need  to  be  increased  eighteen  thousand  times,  by  a  rotary  velocity  one 
hundred  and  thirty-four  times  as  great.  But  on  the  postulate  of  this  theory,  that 
all  space  is  filled  with  similar  matter,  the  gaseous  products  here  considered 
would  be  in  a  state  of  equilibrium,  floating  like  particles  in  an  atmosphere,  so  that 
any  amount  of  centrifugal  force  would  suffice  to  project  them  away  from  the  ro- 
tating body. 


60 


COSMICAL   DUST. 


FIG.  14.    IDEAL  ILLUSTRATION  OF  THE  STREAMS  OP  OUTFLOWING  AND 
INFLOWING  MATTER  UPON  THE  SUN.    AFTER  SIEMENS. 


WORLD-STUFF.  61 

him  that  this  diagram  "  bears  a  very  close  resemblance  to 
the  corona  observed  in  America  on  the  occasion  of  the 
total  eclipse  of  the  sun  on  the  llth  of  January,  1880. 

In  later  communications,  Dr.  Siemens  has  suggested 
other  confirmations  of  his  view,  specifying  the  zodiacal 
light  and  the  spectroscopic  researches  of  Captain  Abney, 
communicated  to  the  British  Association  in  August,  1882, 
demonstrating  the  existence  of  carbon  compounds  proba- 
bly analogous  to  ethyl,  and  at  a  low  temperature,  between 
the  atmosphere  of  the  sun  and  that  of  the  earth.  He 
refers  also  to  the  experiments  made  by  S.  P.  Langley 
(with  the  bolometer),  the  observations  of  Professor 
Schwedoff  (yet  unpublished),  as  well  as  the  older  obser- 
vations of  R.  G.  Carrington  on  the  movements  of  sun- 
spots.* 

Thus,  so  far,  the  phenomenon  of  solar  heat  is  simply 
one  term  in  the  cycle  of  expansion,  dissociation,  condensa- 
tion and  recombination,  indefinitely  repeated.  But  such  a 
process,  even  if  real,  cannot  perpetuate  solar  heat  through 
eternity.  It  simply  delays  final  refrigeration;  since  the 
actual  enormous  radiation  of  the  sun  remains  the  same, 
and  diminishes  daily  by  a  positive  amount  the  aggregate 
of  solar  energy  to  be  employed  in  reproducing  solar  heat.f 

We  ought  not  perhaps,  to  dismiss  Dr.  Siemens'  theory 
without  stating  some  physical  difficulties  which  have  been 
charged  against  it.  The  following  may  be  mentioned: 

(1.)  It  would  introduce  a  disturbing  mass  of  matter 
within  the  solar  si/stem.^  The  attenuated  matter  which 
the  theory  supposes,  would  be  attracted  to  the  sun  and 

*  Siemens,  Comptes  Kendus,  xcv,  771,  10(2,  Oct.  30  and  Nov.  27,  1882. 

tFor  a  thoughtful  paper  touching  the  general  subject  of  "  Matter  in  Space," 
see  Charles  Morris  (Philadelphia),  in  Nature,  xxvii,  319-51,  Feb.  8,  1883.  In  con- 
tinuation of  the  same  line  of  thought,  see  a  paper  by  A.  S.  Ilerschel  in  Nature, 
xxvii,  458,  504-6. 

{  M.  Faye,  Comptes  Jiendus,  Oct. !),  1882,  p.  612;  also  Him,  Comples  Rendus, 
Nov.  6,  1882,  p.  812-4. 


62  COSMICAL    DUST. 

stars,  as  M.  Faye  maintains,  and  would  increase  their  mass. 
It  would  also  constitute,  disseminated  through  space,  an 
important  hindrance  to  the  motions  of  the  heavenly 
bodies.  A  litre  of  air  containing  the  requisite  amount  of 
aqueous  vapor  weighs  at  least  one  gram  at  ordinary  pres- 
sure. At  a  pressure  of  -g-yVoj  which  is  assumed  by  Dr. 
Siemens,  this  will  amount  to  0.0005  gram,  and  a  cubic 
metre  will  weigh  0.005  kilogram.  If  we  consider  the  solar 
system  as  a  sphere  which  will  include  the  planets  as  far  as 
Neptune,  the  weight  of  the  extremely  rarefied  matter 
added  to  the  solar  system  would  be  100,000  times  the 
weight  of  the  sun.*  Such  an  addition  is  physically  inad- 
missible. 

The  first  part  of  this  objection  is  manifestly  disposed 
of  by  the  state  of  spatial  equilibrium  assumed  by  Dr. 
Siemens,  and  which  is  the  express  condition  of  the  equa- 
torial outflow,  since  this  is  a  condition  which  would  pre- 
vent the  gravitation  of  the  matter  toward  the  sun  and 
stars  in  any  other  sense  than  a  possible  diminution  of 
tenuity  in  their  neighborhood.  This  part  of  the  objection 
does  not  apply  to  matter  in  a  state  of  circulation  about 
centres  of  attraction.f 

The  influence  of  such  assumed  vapors  or  gases  as  a 
resisting  medium  upon  the  motions  of  the  heavenly 
bodies,  has  been  more  especially  insisted  upon  by  M. 

*The  matter  added  would  be,  in  kilograms,  $ir  (6400000  X  24000  X  80 )»  x 
0.0005  kilojr. ;  where  the  first  factor  in  the  parenthesis  is  the  earth's  radius  in 
metres,  the  second  is  the  number  of  earth-radii  in  the  earth's  distance  from  the 
sun,  and  the  third  is  the  number  of  times  Neptune's  distance  from  the  sun  ex- 
ceeds the  earth's.  The  weight  of  the  sun,  similarly,  would  be  I^MOOOOOO)' 
X  5.6  X  824000  kilog. ;  where  the  first  number  is  the  radius  of  the  earth  in  deci- 
metres, the  second  the  mean  density  of  the  earth,  and  the  third  the  sun's  mass 
relative  to  the  earth.  The  first  of  these  expressions  is  100,000  times  as  great  as 
the  second,  and  would  imply  that  there  exists  in  the  solar  system  nearly  100,000 
times  as  much  matter  as  has  been  recognized  in  the  delicate  calculations  of 
celestial  mechanics. 

t  Dr.  Siemens,  in  replying  to  M.  Faye's  objections,  holds  that  the  density  of 
the  matter  may  probably  be  reduced  to  one-millionth  of  one  atmosphere. 
Comptes  Rendus,  30  Oct.  1882,  p.  771. 


WORLD-STUFF.  63 

Hirn.*  Referring  to  Laplace's  determination  that  the 
total  retardation  of  the  earth  in  its  orbit  in  three  thousand 
years  cannot  exceed  ninety  seconds,  he  states  that  such 
retardation  would  be  caused  by  a  gaseous  medium  of  such 
tenuity  that  one  kilogram  should  occupy  seven  hundred 
billion  cubic  metres  of  space,  and  that  even  one  ten-quad- 
rillionth  of  a  kilogram  in  a  cubic  metre  (one  kilogram  in 
ten  quadrillion  cubic  metres)  would  suffice  to  sweep  the 
earth's  atmosphere  away  in  a  few  minutes.  To  this  Dr. 
Siemens  replies  by  referring  to  Froude's  experiments 
which  seem  to  show  that  a  solid  moving  through  a  perfect 
fluid  would  experience  no  resistance;!  and  to  the  experi- 
ments of  Messrs.  Fowler  and  Walker  which  demonstrate 
that  the  pressure  of  wind  against  surfaces  is  not  propor- 
proportional  to  their  area;  from  which  it  is  inferred  that 
a  planet  may  move  through  a  rare  and  highly  fluid 
medium  with  very  little  resistance.  Moreover,  according 
to  the  third  law  of  Kepler,  a  diminution  of  tangential 
velocity  should  lead  to  a  diminution  of  distance  from  the 
centre  of  attraction,  and  thus  an  acceleration  of  an  angular 
velocity  which  would  neutralize  the  retardation. 

This  discussion,  it  will  be  noticed,  does  not  particularly 
concern  the  existence  of  small  masses  and  particles  some- 
•what  widely  scattered  in  space. 

(2.)  The  atomic  dissociations  and  associations  would 
neutralize  each  other. \  Granting  that  the  compounds 
dissociated  in  space,  as  Dr.  Siemens  assumes,  by  solar 
and  stellar  radiations,  become  recombined  on  approaching 
the  sun,  the  recombinations  would  become  dissolved  again 
on  attaining  the  full  temperature  of  the  sun's  surface,  as 
the  sun's  heat  is  believed  to  hold  in  a  state  of  dissociation 
the  matters  which  enter  into  his  constitution.  Thus,  the 

*Hirn,  Comptes  Rendus,  xcv,  813-4. 

t  Siemens,  Comptes  Rendus,  xcv,  1040. 

%  M.  G.  A.  Hirn,  Comptes  Rendus,  Nov.  6,  1883. 


64  COSMICAL   DUST. 

heat  given  out  by  recombination  would  be  lost  by  the  final 
decomposition,  and  the  sun  would  gain  nothing. 

This  is  undoubtedly  true  if  the  dissociation  effected  in 
immediate  contact  with  the  sun  is  as  complete  as  that 
effected  in  the  interstellar  spaces.  Dr.  Siemens,  in  reply- 
ing to  M.  Hirn's  objections,*  maintains  that  such  is  not 
the  fact,  since  the  sunjs  photosphere  cannot  be  admitted 
to  possess  a  temperature  above  3000°  C.  It  may  be  fur- 
ther suggested  that  dissociation  in  the  sun's  photosphere 
is  by  no  one  supposed  to  proceed  further  than  the  dis- 
engagement of  the  elements  known  to  chemistry,  while 
recent  science,  as  I  have  shown  (p.  48),  renders  probable 
an  ultimate  atomic  dissolution  in  other  regions  of  space. 

(3.)  The  employment  of  stellar  radiations  in  effecting 
interstellar  dissociation  would  imply  a  more  rapid  dim- 
inution of  the  intensity  of  light  than  the  laic  of  inverse 
squares  of  the  distances  permits.^  The  inherent  luminos- 
ity of  the  heavenly  bodies  must  therefore  be  greater  than 
it  appears;  but  there  exists  no  independent  ground  for 
supposing  the  intensity  of  light  varies  materially  from  the 
law  of  inverse  squares. 

If  this  conclusion  is  admitted,  it  seems  to  furnish  no 
evidence  against  the  theory.  Professor  S.  P.  Langley  t 
has  shown  that  a  large  part  of  the  solar  radiations  ft 
absorbed  by  the  sun's  atmosphere,  and  another  part  by  the 
earth's.  Indeed  it  has  long  been  known  that  the  sensible 
solar  intensity  is  not  in  accordance  with  the  law  of  inverse 
squares  of  the  distances.  Moreover,  the  late  experiments 
of  Captain  Abney  indicate,  on  independent  grounds,  the 
existence  of  an  interplanetary  fluid  of  such  nature  as  the 
Siemens  theory  requires.  And  lastly,  M.  Janssen  has  an- 
nounced as  one  of  the  results  of  his  observation  of  the 

*  Siemens,  Comptes  Rendus,  xcv,  1037-13. 

+  M.  G.  A.  Him,  Comptes  Rendus,  Nov.  6, 1882,  pp.  812-4. 

%  See  especially  an  important  paper  in  Amer.  Jour.  Sci.,  Ill,  xxv.  169-96. 


A   THEOEY.  65 

solar  eclipse  of  May,  1883,  the  "discovery  of  the  Frauen- 
hofer  spectrum  and  the  dark  lines  of  the  solar  spectrum 
in  the  corona,  showing  cosmical  matter  around  the  sun."  * 

Finally,  so  far  as  Dr.  Siemens'  theory  of  the  reproduc- 
tion of  solar  heat  has  any  substantial  basis,  the  doctrine 
of  the  spatial  dissemination  of  ordinary  matter  in  its  ele- 
mental or  atomic  state  receives  confirmation. 

We  may  now  present  a  conspectus  of  the  principal  con- 
ceptions entertained  respecting  the  contents  of  the  inter- 
cosmical  spaces: 

Intercosmical  space  a  vacuum          ...        LAPLACE,  etc. 
Intercosraical  space  a  plenum  (Des  Cartes,  etc.). 
Filled  with  a  peculiar  ethereal  fluid. 

Common  matter  not  generally  diffused     -    YOUNG,  etc. 
Common  matter  existing  as  cosmical  dust     NORDENSKJOLD. 
Filled  only  with  common  matter  excessively 
attenuated. 

(  EULER,      GROVE, 
Meteoroidal  masses  not  specially  important  •<  HUMBOLDT,  HUNT, 

(  SIEMENS. 

Meteoroidal  masses  performing  an  impor- 
tant part. -        THIS  WORK. 

§  7.     A  COSMICAL  SPECULATION. 

Hypothesis  is  the  life-blood  of  investigation.— LOCKYER. 

Nil  tarn  difficile  est 

Quin  quserendo  investigare  possit. — TERENCE. 

Now,  let  us  indulge  in  a  cosmical  speculation.  The 
universal  world-stuff  is  scattered  generally  through  bound- 

*  Paris  Acad.  Sciences,  June  18,  1883,  Nature,  xxviii,  205.  See  the  Siemens 
theory  further  discussed  in  Comptes  Rendus,  Jan.  8,  1883,  p.  79.  Also  by  W.  M. 
Williams:  Current  Discussions  in  Science,  ch.  ii.  1882.  Also,  recently,  by  E.  H. 
Cook  (Phil.  Mag., 400-5,  June,  1883.  Amer,  Jour.  Sci.,  III,xxvi,  67-8,  146)  and  Dr. 
Siemens1  reply  (Phil.  Mag.,  July,  1883,  Amer.  Jour.  Sci.,  Ill,  xxvi,  146-7,  Aug., 
1883).  Siemens'  late  lecture  at  the  Royal  Institution  may  be  found  in  Nature, 
xxviii,  19-21.  The  whole  theory,  together  with  the  various  objections,  is  dis- 
cussed in  a  small  volume  just  published  by  Dr.  Siemens,  entitled,  On  the  Con- 
servation of  Solar  Energy,  London,  111  pp. 

5 


66  COSMICAL   DUST. 

less  space.  Perhaps,  as  Macvicar  and  Saigey*  have 
suggested,  this  primordial  stuff  in  an  extreme  state  of 
attenuation,  is  the  ether,  the  medium  whose  vibrations, 
according  to  Dr.  Young,  striking  the  retina,  produce  the 
sensation  of  light.  Out  of  this  semi-spiritual  substance 
germinate  then  the  molecules  of  common  matter.  It  may 
be  but  varying  modes  of  the  ethereal  atom  as  conceived 
by  Young,  which  give  rise  to  the  sixty  or  seventy  sorts  of 
chemical  atoms,  whose  more  complex  arrangements  con- 
stitute the  molecules  which  make  up  the  molar  aggrega- 
tions of  ordinary  matter.  It  may  be,  on  the  other  hand, 
only  a  highly  attenuated  condition  of  ordinary  matter,  or 
matter  in  a  state  of  ultimate  dissociation.  This  character- 
istic world-stuff,  born  out  of  ether,  in  the  depths  of  space, 
or  however  born,  strewn  through  the  depths  of  space, 
is  acted  upon  by  forces  of  attraction  and  probably  of 
repulsion.  The  material  particles,  either  as  atoms,  or  less 
probably,  as  molecules,  are  drawn  by  mutual  attraction 
into  groups  and  swarms.  Any  central  attractive  force,  as 
of  a  sun  or  planet,  by  causing  the  particles  to  move  in 
converging  lines,  would  cause  them  to  become  approx- 
imated, and  ultimately  aggregated.  Thus,  both  mutual 
attractions  and  centric  movements  would  tend  to  produce 
molar  aggregations  dispersed  through  space.  But  in  the 
presence  of  two  or  more  attractive  centres,  as  in  the 
present  constitution  of  the  cosmos,  it  is  impossible  that 
any  mass  shall  fall  directly  upon  its  centre  of  attraction. 
A  body  A,  Fig.  15,  let  fall  a  hundred  thousand  miles  from 
the  earth  would  not  probably  fall  to  the  earth.  Other 
attractions  besides  that  of  the  earth  would  be  felt  by  it. 
The  resultant  of  these,  the  chief  of  which  would  be  that 
of  the  sun  and  moon,  must,  in  all  probability,  deflect  the 
body  from  a  straight  course  toward  the  earth,  as  in  the 
direction  A  F.  Scarcely  one  chance  in  millions  would 

*  Saigey:  The  Unity  of  Natural  Phenomena.    Translation,  Boston,  1873. 


A   THEORY. 


(57 


exist,  that  the  resultant  of  all  the  attractions  should  coin- 
cide with  the  line  of  descent  to  the  earth.  The  idea 
implies,  either  that  all  the  matter  in  the  universe  be 
arranged  along  one  line  coincident  with  that  connecting 
the  body  with  the  earth,  or  that  it  be  disposed  with  per- 
fect gravitative  symmetry  on  opposite  sides  of  that  line. 
We  must  conclude  that  the  falling  body 
would  be  deflected  from  its  course.  A 
slight  deflection  would  cause  it  to  pass 
one  side  of  the  earth  to  B,  and  even  to 
clear  the  earth's  atmosphere.  It  would 
then  move  a  hundred  thousand  miles  on 
the  side  opposite  to  that  from  which  it 
started.  But  instead  of  continuing  to 
move  in  the  same  direction,  the  earth's 
attraction,  while  it  tends  to  retard  the 
movement  along  the  receding  line,  B  C, 
Fig.  15,  is  exerted  obliquely  to  that 
line,  so  that  after  any  given  interval  of 
time  the  body  is  at  D'  instead  of  D, 
and  when  its  motion  away  from  A  is 
completely  neutralized,  the  body  is  at 
C'  instead  of  C.  It  is  now  in  the  same 
relative  position  as  when  starting  from 
A,  but  possesses  a  certain  amount  of 
motion  in  the  direction  of  C  C'.  As  it 
begins,  therefore,  to  descend  toward  E, 
its  transverse  motion  carries  it  one  side 
of  E  to  D".  But  the  transverse  motion  being  constant  and 
the  descending  motion  accelerated  in  consequence  of  the 
increasing  influence  of  the  earth  E,  the  path  described  will 
be  a  curve.  As  the  transverse  motion  was  generated  while 
the  body  passed  from  B  to  C',  it  will  be  exactly  destroyed 
in  passing  from  C'  to  D".  Thus  the  body  will  return  to  A, 
after  having  completed  the  circuit  of  an  elliptic  orbit.  At 


FIG.  15.  MOTION  or 
A  BODY  IN  THE 
PRESENCE  OP  TWO 
OTHER  BODIES. 


68  COSMICAL   DUST. 

this  point  it  will  be  in  the  same  relative  position  as  at  C' 
and  independently  of  any  external  attraction,  will  proceed 
to  describe  an  orbit  the  second  time,  and  thus  the  process 
will  continue  indefinitely.  The  original  deflecting  force 
may  indeed  continue  to  act,  and  other  perturbating  influ- 
ences may  intervene,  and  it  is  readily  intelligible  that 
subsequent  perturbations  may  bring  the  body  nearer  to 
the  earth,  or  increase  the  distance  between  them.  In 
either  case  the  velocity  of  the  body  will  be  changed.  A 
perturbative  influence  might  even  be  so  adjusted  in 
amount  and  direction  as  to  bring  the  body  to  the  earth. 

It  appears,  therefore,  that  in  the  actual  disposition  of 
the  matter  of  the  universe,  every  body  would  tend  to  cir- 
culate about  every  other  body.  The  body  whose  attrac- 
tions are  most  powerfully  felt  would  become  the  approxi- 
mate centre  of  actual  orbits  for  those  masses  affected  by 
such  superior  attraction.  As  the  sun  is  the  chief  centre 
of  attraction  within  the  solar  system,  most  of  the  matter 
within  the  limits  of  the  system  must  circulate  about  the 
sun.  But  I  see  no  reason  why  meteoric  matter  should  not 
also  circulate  about  the  planets  and  satellites. 

The  actual  conflict  of  attractive  forces  is  not,  however, 
by  any  means,  as  simple  as  in  the  case  supposed.  In  spite 
of  the  continual  tendencv  of  all  bodies  in  space  to  describe 
orbital  motions  about  each  other,  the  conflicting  attrac- 
tions are  so  infinitely  diversified  in  amount  and  direction, 
and  so  variable  with  the  varying  distances  of  bodies,  that 
the  very  fulfilment  of  the  laws  of  motion  results  in  a  net- 
work of  movements  which  is  utterly  incomprehensible,  and 
must  inevitably  precipitate  countless  collisions  of  particles 
and  masses.  The  smaller  the  mass  relative  to  the  masses 
which  control  its  motions,  the  greater  its  liability  to  pre- 
cipitation. 

As  to  the  aggregation  of  cosmical  matter,  I  have  stated 
that,  in  addition  to  the  mutual  attraction  of  the  molecules, 


A   THEORY.  69 

the  convergence  of  their  paths  toward  centres  of  attraction 
must  also  tend  to  the  formation  of  masses  and  swarms  of 
masses  and  particles.  We  have  then  to  picture  indefinite 
space  as  pervaded  by  swarms  of  masses  and  particles  of 
dark  matter.  Each  mass  or  particle  may,  nevertheless,  be 
separated  by  thousands  of  miles,  from  its  nearest  neigh- 
bor in  the  same  swarm.  I  imagine  these  masses  must  be 
continually  passing  between  us  and  the  bright  disc  of  the 
moon;  but  each  mass  is  so  small  relatively,  that  the  light 
of  the  moon  is  not  sensibly  affected  by  it.  The  same  is  true 
of  any  heavenly  body  presenting  a  sensible  disc,  like  the 
planets.  But  the  fixed  stars  are  so  remote  that,  by  per- 
spective, thev  are  reduced  to  points  of  light.  They  must 
be  occulted  then,  by  every  small  mass  of  dark  matter 
passing  between  them  and  us.  All  small  masses  within 
hundreds,  and  perhaps  thousands,  of  miles  of  our  eyes 
would  probably  produce  sensible  effects  upon  the  light  of 
mere  luminous  points,  unless  disguised  by  the  effects  of 
atmospheric  refraction.  Were  there  not  reasons  for  sup- 
posing the  twinkling  of  the  fixed  stars  a  mere  atmospheric 
phenomenon,  it  might  be  worth  while  to  consider  whether 
it  may  not  be  due  to  occupations  by  meteoric  matter, 
especially  as  the  disc-presenting  planets  are  free  from 
scintillation.  On  this  theory,  however,  a  planet  so  remote 
as  to  present  no  sensible  disc  should  also  twinkle  to  some 
extent. 

Swarms  of  small  masses  of  dark  matter  may  therefore  be 
conceived  as  circling  in  numberless  orbits  and  in  all  direc- 
tions about  the  principal  bodies  of  the  solar  system,  but 
in  much  the  greatest  number  about  the  sun.  All  the 
moving  bodies  of  our  system  must  be  continually  pelted 
by  these  cosmical  atoms,  and  the  aggregate  result  of  these 
collisions  must,  in  thousands  or  millions  of  years,  affect 
their  motions.  Supposing  the  motions  of  the  cosmical 
atoms  to  have  no  prevailing  direction,  it  is  evident  that 


70  COSMICAL    DUST. 

the  motions  of  the  planets,  satellites  and  comets  of  our 
system  would  cause  them  to  meet  more  of  these  atoms 
than  the  total  number  which  would  overtake  them.  The 
result  would  therefore  be  a  resistance  to  the  move- 
ment of  these  bodies,  and  the  effect  of  this  would  be 
an  acceleration  of  their  motions  and  a  shortening  of 
their  periods.  I  venture  the  opinion  that  this  cause  is 
a  more  efficient  resistence  than  the  supposed  ethereal 
medium. 

This  simple  conclusion  is  very  fruitful  of  deductive  re- 
sults,* as  Professor  M.  H.  Doolittle  has  shown.  The  resis- 
tance of  an  ethereal  medium  has  always  been  regarded  by 
many  physicists  as  an  inadequate  explanation  of  the  come- 
tary  phenomena  which  have  been  appealed  to  as  evincing 
the  existence  of  a  universal  ether.  But  the  dense  distri- 
bution of  cosmical  matter  may  fairly  be  assigned  as  a 
physical  explanation  of  the  following  otherwise  perplexing 
phenomena:  1.  The  acceleration  of  all  orbital  movements, 
including  those  of  comets,  and  especially  that  of  the  inner 
satellite  of  Mars,  which  revolves  about  its  primary  in  a 
little  over  seven  hours,  while  the  planet  revolves  on  its 
axis  in  about  24  hours,  thus  causing  this  moon  to  rise  in 

*  It  was  independently  enunciated  by  the  writer  in  a  public  lecture,  De- 
cember 3,  1877,  at  Syracuse,  New  York.  The  substance  of  the  lecture  was 
reported  in  the  Syracuse  papers  of  December  4.  The  lecture  was  subsequently 
repeated,  December  7,  at  Groton,  New  York ;  January  4,  at  Pulaski,  New  York ; 
February  5,  at  Cleveland,  Ohio;  February  12,  at  Richmond,  Illinois,  and  Febru- 
ary 16,  at  Lebanon,  Ohio.  I  find  that  a  similar  conception  was  enunciated  at  an 
earlier  date,  by  Rev.  S.  Parsons,  A.M.  "  No  doubt  the  comets  and  all  other 
bodies  meet  with  cosmical  matter,  which  is  'diffused  profusely  throughout  the 
universe,'  according  to  the  observation  of  Laplace.  In  the  course  of  ages  this 
diffused  matter  must  present  a  sensible  resistance  to  the  motion  of  bodies 
through  the  universe."  After  citing  the  abundance  of  meteoroidal  bodies, 
he  added:  "Such  an  amount  of  resistance  would  be  sufficient  to  change  the 
earth's  orbit  from  an  extreme  oval  into  its  present  shape"  (Methodist  Quar- 
terly Renew,  January,  1877,  p.  135).  The  conception  was  subsequently,  though 
independently,  put  forth  by  Mr.  M.  H.  Doolittle,  in  a  paper  before  the  "  Philo- 
sophical Society "  of  Washington  (New  York  Daily  Tribune,  March  6,  1878. 
See  a  further  communication  in  the  same,  April  G,  1878) 


A   THEORY.  71 

the  west  and  set  in  the  east.*  2.  The  irregularities  in 
the  motions  of  comets,  especially  noted  in  Encke's;  since 
meteoroids,  not  being  uniformly  distributed,  would  not 
offer  uniform  resistances.  3.  The  want  of  coincidence  be- 
tween the  planes  of  the  equators  of  the  various  bodies  of 
the  solar  system,  and  between  these  and  the  planes  of 
their  orbits.  This  is  a  group  of  facts  requiring  for  their 
explanation  the  exertion  of  some  force  from  without  the 
svstem.  4.  The  eccentricities  of  the  planetary  orbits. 

While,  however,  the  phenomena  mentioned  under  the 
last  two  heads  may  possibly  be  best  explained  on  the 
hypothesis  of  meteoroidal  resistance,  it  is  admitted  that 
perturbative  attractions  must  probably  be  cited  for  the 
same  purpose,  f 

Returning  to  the  consideration  of  the  constituent  masses 
or  particles  out  of  which  swarms  of  cosmic  bodies  would 
be  constituted,  it  is  manifest  that  each  mass  or  particle 
will  eventually  dispose  itself,  under  the  fixed  action  of  the 
forces  of  matter,  in  some  definite  order.  It  is  manifest 
also,  from  what  has  been  said,  that  each  swarm  will  have  a 
progressive  motion  along  a  path  having  the  essential  char- 
acter of  an  orbit  around  some  dominant  centre  of  attrac- 
tion. If,  as  seems  to  be  the  fact,  an  ethereal  medium,  or 
any  condition  of  interplanetary  matter,  exists  in  space,  it 
opposes  the  movements  of  these  swarms,  by  opposing  the 
motion  of  each  constituent  mass.  But  the  smaller  masses 
—  the  particles  and  molecules  —  would  feel  this  resistance 
to  the  greatest  extent.  They  would  therefore  fall  behind 
the  heavier  masses  and  would  be  most  deflected  toward 
the  attracting  centre.  The  smallest  particles  would  be 
driven  farthest  to  the  rear,  and  dispersed  farthest  from 
the  orbit  of  the  train,  along  the  side  turned  toward  the 

*I  shall  hereafter  show  that  the  solar  tidal  influence  is  also  adequate  to 
produce  such  a  result. 

t  These  two  classes  of  phenomena  are  considered  in  Part  II. 


72  COSMICAL   DUST. 

principal  attraction.  The  swarm  would  present  an  elon- 
gated form  in  which  the  larger  and  heavier  masses  would 
move  foremost,  and  nearest  the  line  of  the  orbit  —  that  is, 
near  the  exterior  skirt  of  the  area  covered  by  the  general 
swarm,  as  in  the  case  of  the  bolide  at  Queengouck  (Fig 
4) — while  the  smaller  ones  would  follow,  in  graduated 
succession,  in  a  long  train  which  would  present  a  fan-like 
expansion  lying  mostly  on  the  inside  of  the  path  of  the 
principal  masses. 

This,  it  may  be  conceived,  is  the  mode  of  aggregation 
of  these  cosmical  matters  in  the  depths  of  space.  Of  course 
the  attractions  which  control  them  are  feeble;  their  move- 
ments are  slow,  the  resistances  are  relatively  inconsider- 
able, and  the  elongation  of  the  swarm  is  correspondingly 
inconspicuous.  What  I  have  described  is  a  tendency 
which  would  be  present.  Sometimes  the  controlling  at- 
traction would  be  only  another  cosmical  swarm.  The  two 
swarms  would  revolve  similarly  about  their  common  centre 
of  gravity;  while  prolonged  resistances  would  cause  their 
slow  approximation  and  final  coalescence  at  the  common 
centre  of  gravity.  Sometimes  the  controlling  attraction 
would  be  exerted  by  a  distant  sun,  around  which  it  would 
slowly  move,  continually  gathering  up  additions  of  matter 
from  the  wide  fields  of  space. 

In  most  cases,  all  controlling  attraction  would  be  feebly 
felt.  These  clouds  of  cosmical  dust  would  float  practically 
poised  in  the  midst  of  space,  and  would  gradually  grow 
by  the  continued  accession  of  new  matter.  Some  of  them 
would  become  aggregates  of  large  dimensions,  and  their 
attractions  would  be  distinctly  felt  by  other  aggregates. 
There  would  be  a  tendency  of  such  aggregates  to  approach 
each  other.  They  might  possibly  approach  along  a  straight 
line,  but  more  probably  some  third  aggregation,  or  some 
distant  sun,  would  deflect  them  into  orbits  about  their 
common  centre  of  gravity,  in  which,  by  prolonged  collis- 


A   THEORY.  73 

ions  of  cosmical  matter,  they  are  brought  to  ultimate 
coalescence  with  each  other.  Or  some  other  attractive 
disturbance  affords  such  a  resultant  of  actions  as  may  bring 
them  more  directly  together.  When  these  larger  aggre- 
gations of  world-stuff  come  together,  the  result  is  an 
aggregation  approaching  the  dimensions  of  the  Her- 
schellian  nebula?.  To  these  attention  will  be  directed  pres- 
ently. 

There  are  other  aggregations  of  very  moderate  magni- 
tude which  chance  to  fall  under  the  influence  of  some  dis- 
tant sun,  toward  which  they  move  through  a  series  of 
ages  —  deflected,  however,  by  lateral  attractions  into  orbital 
paths.  In  the  nearer  neighborhood  of  some  great  attrac- 
tive centre,  the  velocity  of  one  of  these  swarms  is  acceler- 
ated. Its  form  becomes  more  elongated.  The  internal 
movements  of  the  parts  become  more  vigorous;  collisions 
are  sharper,  and  flashes  of  light  are  evolved,  and  the  pos- 
terior train  is  expanded.  Further  influence  exerted  by 
the  central  body  increases  all  these  consequences.  The 
head  of  the  swarm  becomes  permanently  luminous.  The 
long  gathering  swarm  is  now  a  comet.  It  may  have  already 
entered  within  the  precincts  of  our  solar  system.  It  moves 
toward  the  neighborhood  of  our  sun  with  ever-increasing 
velocity  and  brilliancy  and  length  of  train.  Meantime  the 
mysterious  power  —  apparently  repulsive  —  which  the  sun 
exerts  upon  its  constituent  matter  drives  off  infinitesimal 
particles,  but  intensely  luminous,  to  constitute  that  char- 
acteristic appendage  known  as  the  tail.  This  must  be 
distinguished  from  the  train  just  mentioned.  It  rushes 
on;  it  probably  misses  collision  with  the  sun,  is  reined 
back,  and  speeds  by  virtue  of  its  acquired  velocity,  nearly 
in  the  direction  of  a  tangent  to  the  perihelion  curve  des- 
cribed, into  the  remoter  regions  of  our  system. 

When  the  cometary  aggregation  comes  from  an  indef- 
inite distance  beyond  the  confines  of  our  system,  moved 


74  COSMICAL    DUST. 

only  by  the  sun's  attraction,  it  acquires  such  velocity 
as  to  move  in  a  parabolic  curve,  and  hence,  when  it  re- 
cedes from  the  sun  it  can  never  return  unless  its  path  is 
changed  by  some  perturbative  action.  It  is  extremely  im- 
probable that  the  mass  should  move  with  precisely  this 
velocity.  The  planets  of  our  system,  especially  when  the 
comet  passes  in  their  vicinity,  distinctly  impress  its  mo- 
tions. Sometimes  the  action  is  such  as  to  accelerate  its 
velocity,  and  it  then  whirls  around  the  sun  and  departs, 
never  to  return,  along  a  hyperbolic  path.  These  non- 
periodic  comets  probably  proceed  across  the  void  which 
separates  our  system  from  neighboring  systems.  They 
escape  beyond  the  influence  of  powerful  attractions  and 
correspondingly  lay  aside  their  cometary  characteristics. 
Some  of  them  probably  unite  with  other  nebular  aggrega- 
tions. Others,  escaping  through  the  labyrinth  of  attrac- 
tions, move  on  until  another  sun  calls  them  to  itself.  The 
former  experience  may  then  be  repeated;  and  the  com- 
etary body  may  perchance  travel  from  system  to  system 
weaving  the  realm  of  material  existence  into  a  unity. 

But  the  cometary  body  which  ventures  into  our  system 
may  be  still  differently  impressed  by  the  attractions  of  the 
planets.  Its  motion  may  be  retarded.  From  the  moment 
when  its  velocity  is  less  than  that  which  it  would  acquire 
in  falling  from  an  infinite  distance,  it  begins  to  move  in  an 
elliptic  path.  It  is  destined  to  come  around  again  to  the 
same  point.  It  is  a  periodic  comet.  Its  aphelion  is  likely 
to  be  located  near  the  region  where  its  new  path  was  de- 
termined. The  largest  planets  are  of  course  most  likely 
to  exert  this  determinative  influence.  Hence,  of  the  peri- 
odic comets,  nearly  all  have  their  aphelia  near  the  orbit  of 
some  one  of  the  major  planets.  Thus  there  is  a  Jovian 
group  and  a  Saturnian  group.  Most  of  the  periodic 
comets  move  around  the  sun  in  the  same  direction  as  the 
planets;  while,  of  the  whole  number  of  comets  recorded, 


A.   THEORY.  75 

about  half  have  moved  in  the  opposite  direction.  This 
circumstance  is  unexplained,  but  it  must  be  connected  with 
the  direction  of  the  planetary  motions,  or  with  a  general 
vortical  movement  of  the  ethereal  fluid  and  interplanetary 
matters,  which  would  exert  increased  influence  on  the 
slackened  motion  of  comets  turned  into  elliptic  orbits. 

But  now,  the  comet,  domiciled  within  the  system,  is 
subjected  to  constant  perturbative  torments.  Its  eccentric 
orbit  carries  it  across  the  paths  of  the  planets,  and  it  is 
pulled  successively  in  various  directions.  The  enormous 
stress  experienced  in  passing  the  close  vicinity  of  the  sun 
throws  it  into  a  state  of  violent  internal  commotion.  In  a 
body  whose  parts  are  so  incoherent,  dislocation  and  disin- 
tegration begin.  A  constituent  portion  struck  by  another 
has  its  velocity  increased,  and  it  tends  to  move  tangentially 
away  from  the  sun;  the  part  striking  has  its  velocity 
diminished^  and  it  tends  to  move  nearer  the  sun.  The 
effect  is  to  disperse  the  parts.  Wrenched  and  racked  by 
the  distracting  pulls  of  the  sun  and  planets,  it  begins  to 
go  to  pieces.  We  have  seen  comets  going  to  pieces  before 
our  eyes.  The  process  may  be  slow,  but  it  is  real  and  pro- 
gressive. The  train  elongates  and  attenuates,  under  the 
influence  of  the  prolonged  acceleration  of  motion  experi- 
enced on  entering  our  system;  and  at  length  the  disinte- 
gration of  the  parts  proceeds  so  far  that  the  nucleus  loses 
its  luminosity  and  the  swarm  of  constituents  continues  for 
a  time  to  move  about  the  sun  as  a  meteoroidal  train.  Ever 
elongating,  it  may  stretch  at  last  quite  around  its  orbit. 
This  extending  train,  intercepted  by  planetary  atmospheres, 
rains  down  its  substance  in  showers  of  "shooting  stars;" 
but  otherwise,  it  continues  gradually  to  approach  the  sun, 
and  is  ultimately  gathered  as  "solary  fuel"  in  the  central 
fire  of  our  system.* 

*The  bearing  of  Von  Reichenbach's  researches  on  meteorites  and  shooting 
stars  ought  to  have  been  earlier  noticed.  He  finds  all  meteoric  stones  to  be  com- 
pounded of  parts  —  hundreds  or  even  thousands  of  mechanically  separate  constit- 


76  COSMICAL    LUST. 

The  theory  which  claims  a  continuity  between  comets 
and  meteoroidal  trains,  encounters,  it  must  be  confessed, 

uents.  Ordinary  meteoric  stones  are  aggregates  of  smaller  meteoric  stones. 
Both  the  larger  and  the  smaller  are  composed  of  substances  whose  arrangement 
always  follows  a  certain  order.  In  the  centre  are  oxidized  substances,  such  as 
silicates;  upon  these  are  layers  of  sulphurets,  graphite,  and  finally  of  native  iron. 
If  either  class  of  constituents  is  absent,  the  remaining  ones  follow  the  fixed  order. 
Thus  there  has  been  a  growth;  and  the  oxides  or  stony  constituents  are  older 
than  the  metallic.  So,  also,  the  smaller  constituent  meteorites  are  older  than  the 
conglomerates  formed  by  their  aggregation. 

The  formation  and  cementation  of  the  parts  has  not  been  effected  through 
the  agency  of  a  fusing  heat.  If  so,  the  heavier  iron  would  not  have  settled 
around  the  lighter  olivine,  nor  would  graphite  sustain  its  actual  relation  to  mag- 
netic pyrites.  The  primitive  olivine  was  surrounded  by  a  primitive  iron-gas. 
The  primitive  condition  of  all  the  substances  was  gaseous— not  nebulous.  Under 
conditions  once  existing,  the  oxygen  was  active  and  entered  into  its  combina- 
tions, forming  the  primitive  stony  nuclei  of  meteorites.  Later,  the  sulphides, 
and  then  the  graphite,  were  isolated  and  deposited.  Finally,  either  because  the 
oxygen  was  exhausted  or  inactive,  or  because  the  work  was  carried  on  in  a  dif- 
ferent laboratory,  the  unoxidized  iron  was  deposited  in  layers  and  fillings  of  all 
the  interstices.  All  these  layers  are  crystalline. 

Thus,  before  the  existence  of  the  meteorites  which  fall  from  heaven  in  our 
time,  there  must  have  been  a  certain  period  in  which  smaller,  finer,  and  more 
numerous  meteorites  (Meteoritchen)  were  produced — as  "  mere  dust,  starch-flour, 
sand,  grains  to  the  size  of  hail-stones" — these  in  their  microscopic  structure 
composed  of  still  minuter  bodies. 

Shooting-stars  and  fire-balls  are  only  meteoric  bodies,  so  small  as  to  be  dissi- 
pated in  our  atmosphere  on  their  way  to  the  earth.  These  bodies,  large  and 
small,  float  in  space,  and  by  degrees  are  drawn  to  the  earth.  In  the  course  of 
ages  they  must  contribute  important  additions  to  the  earth.  Nickel  and  cobalt, 
he  explains,  are  found  in  all  our  soils.  They  are  not  afforded  by  the  rocks  from 
which  soils  arc  chiefly  formed;  but  they  are  characteristic  constituents  of 
meteorites. 

The  constituent  parts  of  meteorites  present  evidence  of  collision  and  attri- 
tion. They  are  rounded,  as  well  as  angular  and  subangular.  The  very  dust 
worn  from  them  (Reibsel)  is  cemented  together  with  the  larger  kernels  and  balls 
by  means  of  nickellferous  iron.  When  ignited  in  our  atmosphere,  they  are 
again  dissipated  in  vapor.  "Und  man  hatte  sich  dieses  als  einen  feinen  Eegen, 
als  einen  unsichtbarcn  Duft  zu  denkcn,  der  in  ausserst  geringcr  Menge  und  in 
hochst  feiner  Vertheilnng  ohne  Unterlass  sich  aus  dcr  Atmosphiire  auf  unsere 
Meere,  Waider  und  Gefilde  njcdcrscnkt." 

It  is  at  once  apparent  how  the  facts  here  cited  quadrate  with  the  theory  set 
forth  in  the  text. 

These  speculations  of  Von  Reichenbach  are  embraced  in  a  series  of  memoirs 
as  follows:  Veber  die  Zeiffolge  und  die  Bildungswtise  der  niiheren  liestand- 
tfieile  der  Meteoriten,  Poggendorff's  Annalen,  cviii,  452-65,  1859;  Meteoriten  in 
Meteoriten,  id.,  cxi,  353-80,  1860;  Meteorittn  und  Sternschnuppen,  id.,  cxi,  387-401, 
1860;  Die  Slernschnuppen  in  ihren  Bezitkungtn  zur  Erdoberfldchtn,  Id.  cxxiii, 
368-74,  1864. 


A    THEORY.  77 

some  difficulties  not  yet  fully  explained.  The  common 
representation  is  that  the  train  of  the  meteoroidal  swarm 
is  to  be  identified  with  the  tail  of  the  comet;  but  this  is 
evidently  inadmissible,  because  the  comet's  tail  precedes 
during-  the  retreat  from  the  sun,  and  because  the  velocity 
implied  in  the  distant  parts  of  the  tail  while  passing  peri- 
helion is  entirely  inadmissible  as  an  actual  translation  of 
matter,  and  perhaps  also,  in  consequence  of  its  considera- 
ble luminosity  at  great  distances  from  the  sun.  Again, 
the  luminosity  of  the  head  itself,  at  a  distance  as  great  as 
Mars  or  Jupiter  from  the  sun,  cannot  be  due  to  the  intense 
heat  of  the  sun's  rays,  as  might  be  the  case  at  perihelion. 
The  amount  of  collision  among  the  parts,  in  an  aggrega- 
tion containing  so  little  matter  as  a  comet,  can  with  diffi- 
culty be  conceived  as  imparting  the  permanent  luminosity; 
and  the  query  arises  whether  the  phenomenon  is  not  due 
to  some  other  action  than  heat.  It  is  supposable  that  the 
light  of  the  tail  is  wholly  reflected,  as  we  know  most  of  it 
is,  in  the  nearer  vicinity  of  the  sun.  The  nuclei  are  well 
known  to  contain  incandescent  gases  when  they  have  been 
examined  on  their  visit  to  the  sun's  neighborhood;  but  one 
•would  expect  masses  so  limited  in  amount  to  lose  their 
thermal  luminosity  in  receding  toward  their  aphelia.* 

The  phenomena  of  the  tail,  especially  in  the  vicinity  of 
aphelion,  are  such  as  would  result  if  we  could  conceive  the 
nucleus  of  the  comet  surrounded  by  an  aura  extending  on 
all  sides  as  far  as  the  remotest  limits  of  the  tail,  and  could 
recognize  the  tail  as  merely  a  luminous  shadow  cast  by  the 
nucleus  in  intercepting  certain  radiant  energy  proceeding 

*  One  is  reminded,  in  this  connection,  of  the  analogies  between  cometary 
tails,  the  streamers  of  the  aurora  borealls  and  the  trains  of  radiant  matter  in  the 
tubes  employed  by  Professor  Crookes  (see  references,  p.  49).  Without  affirming 
a  '•  fourth  state  of  matter,''  or  even  the  doctrine  of  the  continuity  of  states,  it  is 
apparent  that  the  attenuation  of  the  medium  in  which  the  phenomena  of  "ra- 
diant matter"  are  revetiled,  is  quite  analogous  to  that  of  the  medium  in  which 
the  northern  streamers  dance,  or  in  which  the  tails  of  conu  ts  execute  motions  of 
such  mysterious  velocity. 


78  COSMICAL   DUST. 

from  the  sun.*  Perhaps,  after  all,  the  theory  is  the  most 
plausible  one  which  contemplates  the  tail  as  a  vapor  of 
some  unknown  constitution,  perpetually  driven  off  by  some 
mysterious  repulsive  power  of  the  sun,  perhaps  electric, 
growing  more  intense  with  diminished  distance.  The  tail 
would  be,  therefore,  not  a  material  form  moving  with  the 
comet,  but  something  perpetually  renewed,  while  the  older 
and  more  distant  emanations  disappear  from  visibility. 
M.  Faye,  in  this  view,  compares  the  comet's  tail  to  the 
smoke  rising  from  the  pipe  of  a  transatlantic  steamer, 
which,  though  continually  changing  molecularly,  is  the 
same  phenomenon  all  the  way  from  Havre  to  New  York. 

Thus  we  glimpse  in  outline  the  cosmic  conception  which 
forms  the  ground  of  the  reasonings  and  speculations  of  the 
present  work.  The  world  in  which  we  live  is  to  be  ac- 
counted for,  and  the  method  of  its  evolution  explained. 
Geology  undertakes  to  write  some  chapters  of  its  past 
history;  but  a  true  geology,  in  a  broader  sense,  will 
unfold  many  other  glowing  chapters,  which  mere  induc- 
tive science  could  never  make  known.  We  take  up  the 
details  of  the  first  chapters  of  inductive  geology  with  the 
feeling  that  much  has  been  left  out.  They  present  only 
the  beginning  of  the  last  act  of  the  drama.  But  our 
intelligence  presses  back  in  search  of  a  real  beginning  of 
the  world;  and  even  if  scientific  inquiry  is  doomed  to 
failure  in  its  search  for  an  absolute  beginning,  it  is  a 
noble  impulse  and  an  inalienable  prerogative  which  sanc- 
tion the  effort  to  press  as  far  as  possible  toward  the  abso- 
lute beginning.  I  doubt  if  we  can  at  present  fix  upon  a 
starting  point  antecedent  to  that  diffused  chaotic  condi- 
tion of  world-stuff  of  which  so  many  glimpses  have  been 
revealed  to  the  mind's  eye.  I  strongly  believe  we  have 

*See  W.  A.  Norton  on  comets  in  Amer.  Jour.  Sd.,  II,  xxvii,  86, 103;  xxix,79, 
383-6.  See  also  Bredechin's  researches  on  the  tails  of  cdinets,  Annalts  de  I'Ob- 
servatoire  de  Atoscou,  vols.  iil-vi,  and  M.  Faye's  memoirs,  Comptes  Rendus,  Aug. 
1  and  8,  1881. 


A   THEORY.  79 

caught  glimpses  of  the  mode  of  formation  of  world  germs. 
It  remains  then,  to  trace  their  development,  their  maturity 
and  their  decadence.  This  will  lead  us  to  the  study  of 
nebular  life,  and  the  nature  of  the  continuity  existing 
between  nebulae,  suns  and  planets;  and  to  contemplate 
finally  those  ulterior  planetary  conditions  which  disclose 
the  data  of  a  geology  of  the  future,  and  complete  the 
natural  cycle  of  cosmic  existence. 


CHAPTEE  II. 

NEBULAR    LIFE. 

Que  dire  de  ces  espaces  immenses  et  des  astres  qui  les  remplissent?  Que 
penser  de  ces  etoiles  qui  sont  sans  doiite,  comme  notre  Soleil,  des  centres  de 
lumicre,  de  chaleur  et  d'activite,  destine's  comme  lui,  a  entretenir  la  vie  d'une 
foule  dc  cre"aturcs  de  toute  espece? — Le  padre  SECCHI. 

THE  irresolvable  nebulje,  as  I  have  endeavored  to  indi- 
cate, are  probably  nothing  but  stupendous  examples 
of  meteoric  or  cosmical  clouds  which  have  become  heated 
to  such  an  intensity  that  their  matter,  or  some  of  it,  exists 
as  vapor,  though  it  is  not  necessary  to  suppose  that  the 
portions  subjected  to  observation  sustain  a  temperature  of 
relatively  high  intensity.  At  the  same  time,  such  is  their 
enormous  mass  that  their  interiors  must  be  compressed  to 
many  thousand  times  the  density  of  the  exterior  por- 
tions. These  prodigious  accumulations  may  have  been 
gathered,  by  the  mutual  attractions  of  the  parts,  from 
wide  contiguous  fields  of  space.  They  are  not  drawn  out 
into  meteoric  rings  or  partial  rings  surrounding  our  sun, 
because  they  are  so  immensely  remote  as  to  be  little 
affected  by  the  solar  attraction,  and  are  relatively  so  vast 
as  to  possess  controlling  power  of  their  own.  They  have 
not  formed  meteoric  rings  around  other  suns,  because 
they  are  equally  remote  from  them  and  equally  exceed 
them  in  mass.  According  to  the  conception  from  which 
we  reason,  the  nebular  aggregations  discernible  within 
our  field  of  vision — both  resolvable  and  irresolvable — lie 
dispersed  through  unlimited  space.  Many — perhaps  most 
or  even  all  of  them  —  float  within  the  bounds  of  that 
starry  universe  whose  nearer  members  constitute  our  vis- 


NEBULAR    HEAT.  81 

ible  firmament.  But  if  with  Herschel  we  set  limits  to 
our  starry  firmament,  we  may  readily  believe  that  many 
of  these  nebular  aggregations  lie  far  beyond  the  distance 
of  its  remotest  star.  According  to  Father  Secchi,  the 
depths  of  the  cosmos  are  unfathomable.  All  the  stars 
constituting  the  firmament  surrounding  our  sun  are  but  a 
patch  of  the  boundless  Milky  Way,  and  if  seen  from  a  cer- 
tain distance  would  appear  only  as  a  white  spot  in  the 
Milky  Way  itself.  In  any  view  of  the  relative  positions  of 
the  nebulae,  the  cosmic  organisms  of  infinite  space  lie  separ- 
ated by  such  enormous  intervals  that  while  one  of  these 
clouds  of  world-stuff  must  feebly  feel  the  attractions  of 
other  material  masses,  it  may  be  regarded  as  practically 
removed  from  their  influence.  We  have  now  to  inquire, 
what  will  be  its  behavior  ? 

§  1.     NEBULAR  HEAT. 

1.  Heat  Produced  by  Refrigerative  Contraction. — At 
an  earlier  period,  we  must  assume,  the  gathering  nebulous 
matter  was  cold  and  non-luminous.  Accordingly  we  may 
conjecture  that  countless  germs  of  future  nebulas  exist  in 
space,  which  have  not  yet  been  discovered,  because  not  yet 
heated.  By  what  means  a  nebulous  mass  becomes  so 
heated  as  to  be  self-luminous,  is  supposed  by  some  physi- 
cists to  be  demonstrated  by  the  uniform  evolution  of  heat 
in  every  body  which  undergoes  condensation  by  pressure. 
Helmholz,  Peirce,  Sir  William  Thomson  and  others  have 
calculated  the  amount  of  heat  which  must  be  evolved  dur- 
ing the  condensation  of  the  sun  from  such  a  volume  as 
would  fill  the  orbit  of  Neptune.*  Young  and  others  have 
suggested  that  the  heat  of  the  incandescent  nebula  whose 

*Mr.  Maxwell  Hall  has  calculated  that  to  supply  the  sun's  loss  of  heat 
from  radiation,  it  is  only  necessary  to  contract  39.15  metres  a  year.  This  would 
require  18,263  years  to  effect  a  shrinkage  of  one  second  in  the  sun's  diameter 
(Monthly  Notices,  Astronomical  Society,  1874,  837). 


82  NEBULAE    LIFE. 

condition  is  revealed  by  the  spectroscope,  has  been  liber- 
ated during  a  process  of  spontaneous  condensation.  If 
this  explanation  is  legitimate  and  sufficient,  it  is  unneces- 
sary to  seek  farther  for  the  cause  of  nebular  luminosity. 

The  explanation,  however,  seems  to  be  a  suitable  sub- 
ject for  examination.  At  first  glance  it  would  seem  to 
contradict  reason.  It  is  quite  apparent  that  if  the  nebula 
is  internally  in  equilibrio,  such  heat  would  be  evolved  if 
the  condensation  were  effected  by  the  application  of  force 
from  without  —  as  the  air  is  heated  in  a  condensing  syr- 
inge, or  iron  under  a  hammer.  But  a  spontaneous  con- 
densation excludes  the  application  of  extraneous  force. 
It  means  a  condensation  under  the  influence  of  forces  resi- 
dent in  the  mass.  These  forces  as  far  as  this  question  is 
concerned,  are  central  attraction,  molecular  attractions 
and  repulsions,  and  heat.  At  a  given  moment,  in  a 
nebula  internally  in  equilibrium,  the  central  attraction  of 
the  parts  is  exactly  balanced  by  the  repulsive  or  expansive 
force  due  to  the  amount  of  heat  belonging  to  the  body. 
Without  any  change  in  the  relative  intensities  of  these 
shrinkage  and  expansive  forces,  the  volume  of  the  nebula 
must  necessarily  remain  unchanged.  Its  temperature,  of 
course,  remains  unchanged.  If,  at  any  moment,  its  tem- 
perature is  above  that  of  surrounding  space, it  must  radiate 
a  portion  of  its  heat.  A  certain  amount  of  contraction 
exactly  corresponding  with  the  amount  of  heat  lost,  will 
ensue.  The  equilibrium  between  the  reactionary  and  the 
central  attractive  forces  is  restored,  and  the  volume  must 
remain  unchanged  until  farther  loss  of  heat  takes  place. 
Thus,  the  condensation,  supposing  always  that  the  aggre- 
gative process  is  completed,  can  only  respond  to  loss  of 
heat.  No  condensation  can  take  place  except  as  a  conse- 
quence of  such  loss.  The  condensation,  therefore,  cannot 
increase  the  heat.  If,  during  a  process  of  condensation, 
the  temperature  is  raised,  this,  in  the  light  of  the  princi- 


NEBULAR   HEAT.  83 

pies  stated,  must  be  the  consequence  of  force  applied 
from  without. 

Obviously,  there  is  a  period  in  the  aggregation  of  a 
nebula  during  which  the  central  attraction  may  be  re- 
garded as  crowding  the  constituents  together;  and  during 
this  period,  heat  would  be  developed.  An  equilibrium 
being  attained  between  this  attraction  and  the  repulsive 
forces,  the  nebula  will  have  reached  the  normal  state  at 
which  its  evolutions  begin.  Some  nebulae,  undoubtedly, 
exist  in  the  prenormal  state,  and  may  be  growing  heated 
by  condensation  —  but  it  has  not  seemed  to  me  that 
all  nebulae  must  be  supposed  in  this,  condition.  Perhaps 
the  greater  number  must  be  in  some  stage  in  which  the 
condensation  is  conditioned  and  measured  by  the  cooling. 

Professor  Simon  Newcomb  in  his  admirable  work  on 
"  Popular  Astronomy "  (pp.  507,  508),  speaking  of  the 
possible  cause  of  the  perpetuation  of  the  sun's  heat,  says: 

-"As  his  globe  cools  off  it  must  contract,  and  the  heat 
generated  by  this  contraction  will  suffice  to  make  up 
almost  the  entire  loss."  That  is,  cooling  causes  contrac- 
tion, and  contraction  causes  heat;  therefore  cooling  catises 
heat.  But  further:  "  By  losing  heat  a  gaseous  body  con- 
tracts, and  the  heat  generated  by  the  contraction  exceeds 
that  which  it  had  to  lose  in  order  to  produce  the  contrac- 
tion."* This  curious  paradox  was  rendered  rational  by  a 
learned  investigation  published  by  Mr.  J.  Homer  Lane,  of 
Washington,!  the  gist  of  whose  paper  is  thus  summarized 
by  Professor  Newcomb:  "If  a  globular  gaseous  mass  is 
condensed  to  one-half  its  primitive  diameter,  the  central 
attraction  upon  any  part  of  its  mass  will  be  increased  four- 
fold, while  the  surface  upon  which  this  attraction  is  exer- 

*  Then  certainly  the  body  is  growing  hotter  and  consequently  expanding 
while  it  contracts  from  cooling! — unless,  meantime,  the  surplus  heat  is  lost  by 
radiation. 

•^American  Journal  of  Science  for  July,  1870. 


84  NEBULAR   LIFE. 

cised  will  be  reduced  to  one-fourth.  Hence  the  pressure 
per  unit  of  surface  will  be  increased  sixteen  times,  while 
the  density  will  be  increased  only  eight  times.  Hence  if 
the  elastic  and  gravitating  forces  were  in  equilibrium  in 
the  primitive  condition  of  the  gaseous  mass,  its  tempera- 
ture must  be  doubled  in  order  that  they  may  still  be  in 
equilibrium  when  the  diameter  is  reduced  one-half." 

For  the  sake  of  further  elucidating  this  curious  paradox 
let  us  enunciate  the  points  in  the  following  form: 

(1.)  If  the  diameter  is  reduced  one-half,  the  density  is 
eight  times  as  great,  since  the  same  matter  is  compressed 
into  one-eighth  the  volume. 

(2.)  The  intensity  of  attraction,  and  therefore  the  total 
attraction,  at  the  new  surface,  is  four  times  as  great,  since 
the  same  amount  of  matter  attracts  at  one-half  the  former 
distance  from  the  centre  of  gravity. 

(3.)  But  the  new  surface  is  only  one-fourth  the  original 
surface;  hence  each  unit  of  new  surface  must  receive  six- 
teen times  the  attraction  (pressure)  of  a  unit  of  the 
original  surface. 

(4.)  If  the  pressure  is  sixteen  times  as  great,  and  the 
density  is  only  eight  times  as  great,  the  elastic  force  to 
equilibrate  the  excess  of  pressure  must  be  twice  as  great. 

Now,  if  that  elastic  force  is  wholly  heat,  the  shrunken 
body  must  have  twice  the  heat  of  the  original  body;  and 
that  is  what  the  contractional  theory,  as  commonly  stated, 
concludes;  and  in  this  way  a  surplus  of  heat  may  be  radi- 
ated, and  still  a  constant  or  even  increasing  temperature 
maintained. 

But  the  new  body  has  not  twice  the  heat  of  the  old 
body,  since,  necessarily,  a  constant  radiation  of  heat  has 
been  taking  place. 

If,  by  hypothesis,  the  original  body  has  shrunken  to 
half  its  dimensions,  and  by  observation,  some  of  its  heat 
is  known  to  have  been  lost,  the  new  body  will  be  half  the 


NEBULAE   HEAT.  85 

diameter  of  the  old,  without  having  twice  the  amount  of 
heat.  That  is,  the  elastic  force  which  equilibrates  the 
excess  of  pressure  is  in  part  at  least,  something  besides 
heat. 

This  is  also  evident  from  the  consideration  that  the 
body  is  supposed  to  shrink  simply  in  consequence  of  cool- 
ing; and  the  supposition  of  an  increase  of  heat  is  in  con- 
flict with  the  assumed  premise.  A  body  cannot  be  growing 
hotter  in  consequence  of  a  shrinkage  produced  by  growing 
colder.  It  may  have  some  of  its  heat  restored,  and  thus 
its  cooling  retarded.  To  assume  that  the  temperature  is 
not  lowered  in  correspondence  with  a  decrease  of  volume 
when  the  pressure  is  constant,  is  in  conflict  with  the  well 
established  law  of  Charles. 

But  it  is  assumed  that  the  heat  developed  by  shrinkage 
is  lost  through  radiation  in  the  meantime.  If  only  the 
excess  developed  is  lost,  the  body  remains  of  the  same 
temperature  as  at  first,  and,  therefore,  is  not  cooling,  as 
the  premise  demands. 

Also,  if  the  excess,  or  more  than  the  excess  of  heat  is 
radiated,  then  there  is  less  elastic  force  in  the  form  of 
heat  than  in  the  original  body,  while  the  reasoning  requires 
twice  as  much. 

It  seems,  therefore,  that  the  doubled  elastic  force 
required  in  the  shrunken  body  to  equilibrate  the  increased 
pressure  must  be  something  besides  heat.  May  it  not  be 
simply  a  repulsion  among  the  molecules,  which  varies 
according  to  some  law  of  the  distance? 

Now,  the  following  seems  to  me  to  be  a  correct  sum- 
mary statement  of  the  whole  case: 

(1.)  The  falling  together  of  the  particles  and  masses 
will  generate  heat;  and  the  generation  will  progress  as 
long*  as  the  parts  continue  to  descend  toward  the  common 
centre  of  gravity. 

(2.)    The  heat  thus  developed  will  be  active,  sensible 


86  NEBULAR    LIFE. 

heat.  The  sensible  temperature  resulting  must,  however, 
be  discriminated,  as  always,  from  the  total  thermal  potency 
in  the  body. 

(3.)  The  centric  movement  of  the  parts  will  cease  when 
the  elastic  forces  become  equal  to  the  gravitating  tendency 
of  the  parts.  The  nebula  is  then,  disregarding  the  effect 
of  progressive  radiation,  in  a  state  of  internal  equilibrium. 

(4.)  Subsequent  loss  of  heat  will  permit  the  parts  again 
to  fall  together,  until  their  approximation,  or  in  other 
words,  the  work  done  by  the  descending  parts,  develops 
an  increased  amount  of  elastic  force,  partly  heat,  which 
will  again  equilibrate  gravity  even  at  its  now  increased 
intensity. 

(5.)  The  loss  of  heat  diminishes  the  total  amount  of 
heat,  and  diminishes  the  temperature;  but  the  descent  of 
the  parts  will  necessarily  develop  a  new  amount  of  heat, 
and  partially  restore  the  temperature  and  volume. 

(6.)  The  former  temperature  cannot  be  completely 
restored,  for  that  was  a  temperature  which  maintained 
the  mass  at  the  volume  which  it  had  before  the  contrac- 
tion; and  by  hypothesis,  contraction  is  a  fact. 

(7.)  As  the  newly  developed  heat  must  fail  to  equili- 
brate the  newly  increased  pressure,  the  equilibrium  must 
be  completed  by  some  reactionary  force  which  would 
exist  at  absolute  zero  of  temperature. 

(8.)  The  actual  volume  will  lie,  therefore,  between  the 
original  volume  and  that  which  would  have  resulted  if 
contraction  had  not  developed  heat;  and  the  actual  tem- 
perature will  lie  between  the  original  temperature  and 
that  which  would  have  resulted  if  no  heat  had  been 
developed  by  contraction. 

(9.)  It  is  true,  then,  that  contraction  develops  heat,  and 
that  its  development  delays  final  refrigeration; — that  is, 
the  progress  toward  final  refrigeration  is  not  as  rapid  as 
the  amount  of  radiated  heat  implies.  But  it  is  not  true 


NEBULAR   HEAT.  87 

that  contraction  (from  cooling)  can  have  developed  the 
whole  amount  of  heat  at  any  time  existing  in  the  mass, 
or  can  even  maintain  a  body  at  a  constant  temperature. 

2.  Changes  in  the  Forms  of  Nebulw. — From  this 
quite  abstruse  question  let  us  return.  If  we  have  to  con- 
clude that  a  shrinkage  or  condensation  in  a  gaseous  mass 
whose  parts  are  maintained  in  a  state  of  mutual  equilib- 
rium is  physically  incapable  of  developing  the  heat  which 
we  find  existent  in  nebulas,  then  we  have  to  inquire,  what 
is  the  external  cause  which  develops,  maintains  or  increases 
the  heat  of  a  nebulous  mass  in  space? 

As  I  have  stated,  we  may  reasonably  assume  the  cos- 
mical  dust  promiscuously  distributed.  But  mutual  attrac- 
tions would,  sooner  or  later,  result  in  conglomerations  of 
relatively  moderate  size.  This  process  would  be  accom- 
panied by  a  transformation  of  gravitational  energy  into 
thermal,  and  this  would  be  continued  until  the  internal 
elastic  forces  should  be  able  to  equilibrate  the  gravita- 
tional forces.  The  nebula  would  have  assumed  its  normal 
condition.  Every  nebulous  conglomeration  would  still  be 
attracted  by  any  other — both  the  larger  and  the  smaller. 
The  process  of  conglomeration  would,  therefore,  tend  to 
continue  indefinitely.  Those  immense  nebulae  would  finally 
be  developed  which  have  attracted  the  attention  of  astron- 
omers. The  larger  masses  having  drawn  to  themselves  all 
the  smaller  masses  in  their  several  regions  of  space,  the 
intervening  spaces  would  seem  to  be  comparatively  free 
from  nebulous  matter. 

Now,  I  would  suggest  that  the  process  of  conglomera- 
tion may  explain  the  irregularities  in  the  forms  of  certain 
nebulte.  The  protuberant  portions,  the  salient  angles,  the 
denser  bands,  the  luminous  spots,  may  all  be  conceived  as 
precipitated  nebulous  masses  which  have  not  yet  had  time 
to  become  completely  coalesced;  or  they  are  nebulous 
masses  which  have  been  pushed  out  of  symmetry  or  homo- 


88  NEBULAR    LIFE. 

geneity  by  the  impact  of  a  foreign  mass.  We  have  gazed 
on  those  irregular  forms,  like  the  nebula  in  Orion,  and  the 
Magellanic  Clouds,  and,  mindful  of  the  law  of  matter  by 
which,  when  free  to  move  upon  itself,  it  assumes  the 
spherical  form,  we  have  deemed  it  mysterious  that  such 
irregularity  could  persist.  Now,  on  the  theory  just  enunci- 
ated, the  irregularity  must  arise;  but  there  is  nothing  to 
cause  it  to  persist.  The  irregular  nebula  must  be  in  pro- 
cess of  assuming  some  symmetrical  shape.  Its  destined 
shape  is  not  already  assumed,  because  the  history  of  its 
evolutions  began  in  finite  time.  The  nebula  has  not  yet 
had  time  sufficient  to  undergo  its  changes.  Its  destined 
evolution  must,  therefore,  be  in  progress  at  this  moment. 
Now,  it  is  gratifying  to  be  able  to  announce  that  changes 
have  been  noted  in  nebular  phenomena.  "  Some  nebulas 
have  vanished;  others  have  appeared  where  formerly  no 
nebulosity  had  been  recognized."  Not  a  few  changes  have 
been  witnessed  in  the  forms  of  nebulas.  The  Magellanic 
Clouds,  according  to  Sir  William  Herschel,*  have  under- 
gone important  changes  during  a  human  lifetime.  The 
great  Nebula  in  Orion  (Figure  6)  is  now  generally  admit- 
ted to  be  in  process  of  change. f  The  nebula  surrounding 
the  remarkable  variable  star  Eta  Argus  is  subject  to  great 
changes.^  The  Omega  Nebula  (H.  2,008)  through  the 
careful  researches  of  Professor  E.  S.  Holden,  is  shown  to 
be  probably  undergoing  internal  changes.§  The  various 

*  Herschel,  Phil.  Trans,  1811.  So,  also,  Sir  John  Herschel:  "Speaking 
from  my  own  impressions,  I  should  say  that  in  the  structure  of  the  Magellanic 
Clouds  it  is  really  difficult  not  to  believe  we  see  distinct  evidence  of  the  exercise 
of  such  a  power  of  aggregation:"— Address,  British  Association,  1845. 

tSchellen:  Spectral  Analysis,  371 ;  Sir  W.  Herschel,  Phil.  Tran$.,  1811; 
Otto  Strnve,  Monthly  Notices  Astronom.  Soc  ,  London,  March  14,  1856,  vol.  xvi, 
p.  189;  Gautier,  Archives  des  Sciences  Physiques  et  Naturelles  de  Geneve.  1862, 
translated  in  Smithsonian  Report,  1863,  299 ;  Secchi,  Comptes  Rendus,  Ixv,  p.  C43, 
Ixvi,  63. 

t  F.  Ahhot,  Proc.  Roy.  Astron.  Soc.,  Nov.  13, 1863 ;  Am.  Jour.  Set.,  II,  xxxvii, 
294-6. 

§  Holden :  On  Supposed  Changes  in  Nebula  M.  17,  Am.  Jour.  3d.,  Ill,  xi,  341- 
61,  May,  1876. 


NEBULAR   HEAT.  89 

drawings  of  this  nebula,  from  that  of  Herschel  in  1833 
to  that  of  Lasell  in  1862  (Fig.  16),  and  that  of  Trouvelot 
and  Holden  in  1875  (Fig.  17),  seem  to  indicate  that  the 
eastern  or  omega-shaped  portion  of  the  nebula  has  under- 
gone considerable  change  in  respect  to  the  stars  in  closest 


FIG.  16.— THE  OMEGA  NEBULA.    FROM  A  DRAWING  BY  LASELL 


contiguity  to  it.  Professor  Holden  says:  ''These  draw- 
ings show  that  the  western  end  of  this  nebula  has  moved 
relatively  to  its  contained  stars  from  1833  to  1862,  and 
again  from  1862  to  1875,  and  always  in  the  same  direc- 
tion." Meantime  the  conspicuous  "streak"  or  wing  ex- 
tended toward  the  east  has  not  moved  in  reference  to  the 


90 


NEBULAR   LIFE. 


NEBULAR   HEAT.  91 

stars.  The  parts  of  this  nebula  are,  therefore,  in  motion 
with  reference  to  each  other.  The  Trifid  Nebula  has  been 
shown  by  the  same  investigator  *  to  possess  a  proper 
motion  in  reference  to  the  stars.  This  nebula  consists  of 
three  nebulosities  separated  by  dark  passages,  as  shown  in 
Fig.  18.  In  the  middle  of  the  intervening  space,  from 


Fio.  18.— THE  TRIFID  NEBULA. 
FROM  A  DRAWING  BY  TROUVELOT. 

1784  to  1833,  was  situated  a  distinct  triple  star;  but 
"from  1839  to  1877  the  triple  star  was  not  centrally  situ- 
ated between  the  three  nebulosities,"  but  involved  in  one 
of  them.f 

*  E.  S.  Holden,  Am.  Jour.  ScL,  III,  xiv,  433-58. 

t  On  the  motion  of  nebulae  in  the  line  of  sight,  see  W.  Huggins,  Proc.  Royal 
Soc  ,  March,  1874.  Seven  nebulae  observed  indicate  a  motion  in  reference  to  the 
earth  ranging  from  one  to  fourteen  miles  a  second. 


92  NEBULAR    LIFE. 

We  may  rest  assured  that  fleecy  masses  like  the  nebulae, 
when  presenting1  forms  as  unsymmetrical  as  some  of  them, 
cannot  be  reposing  in  a  state  of  finality.*  We  may 
wonder  that  these  changes  should  be  so  slow  that  the 
nebula  seems  almost  in  a  fixed  condition.  That  apparent 
slowness  of  change,  we  may  be  certain,  is  a  consequence 
of  the  inconceivable  remoteness  of  those  bodies.  The 
star  known  as  1830  Groombridge  is  moving  through  our 
firmament  at  the  rate  of  200  miles  a  second;  yet  it  re- 
quires 123  years  to  move  over  an  angular  space  equal  to 
the  diameter  of  the  moon.  The  diameters  of  some  visible 
nebulas  are  probably  greater  thau  the  distance  which  sep- 
arates us  from  the  nearest  star.  Motion  in  masses  so 
immense  and  so  remote  must  necessarily  seem  deliberate. 
The  earth  takes  twenty-four  hours  to  turn  over;  the  sun 
requires  twenty-five  days;  a  flea  needs  but  a  small  fraction 
of  a  second.  The  moon  revolves  around  its  orbit  in 
twenty-seven  days,  but  Uranus  consumes  the  time  of 
three  generations  of  men.  Yet  the  diameter  of  the  orbit 
of  Uranus  may  easily^  be  less  than  the  space  separating 
two  distinguishable  points  of  star-dust  in  a  resolvable  neb- 
ula. I  think,  therefore,  we  are  not  stretching  the  physi- 
cal probabilities  in  attributing  the  irregularities  of  the 
nebula?  to  the  process  of  conglomeration;  and  in  antici- 
pating that  the  shapeless  nebula  in  Orion  will  one  day 
have  assumed  a  symmetrical  form. 

3.  Heat  Arising  from,  the  Aggregative  Process. — The 
thought  must  already  have  suggested  itself  to  the  reader 
that  the  process  of  conglomeration  affords  an  explanation 

*For  mention  of  other  supposed  changes,  see  the  memoir  of  Gautier, 
already  cited.  On  the  general  question  of  nebular  changes  see  Arago:  Astro- 
nomie  populaire.  In  some  instances  changes  of  brightness  have  been  observed 
which  are  far  more  striking  than  any  observed  changes  of  form.  The  small 
nebula  in  Taurus,  discovered  by  Hind  in  1852,  had  disappeared  in  1861,  and  was 
not  again  visible  till  1868,  after  which  it  again  disappeared.  So  conversely,  the 
temporary  star  discovered  by  Dr.  Schmidt  in  the  Swan,  gradually  faded  into  the 
appearance  of  a  planetary  nebula. 


NEBULAR   HEAT  93 

of  the  intense  heat  which  vaporizes  its  substance,  and 
causes  it  to  yield  a  spectrum  of  bright  lines.  As  the  sud- 
den compression  of  a  portion  of  atmospheric  air  yfelds 
heat  sufficient  to  ignite  tinder,  or  fuse  and  volatilize  a  de- 
scending meteor-mass,  so  the  precipitation  of  one  planet 
upon  another  would  liberate  sufficient  heat  to  reduce  them 
both  to  a  state  of  fusion,  or  even  of  vapor.  Still  more 
must  the  intensest  heat  be  generated  by  the  impact  of  two 
nebulous  masses,  one,  or  both  of  which  together,  may  em- 
brace more  matter  than  all  our  planets  and  the  sun  com- 
bined—  as  much  even  as  the  matter  of  our  entire  visible 
firmament  of  stars.*  One  experiences  a  distinct  feeling 
of  relief  in  the  discovery  of  such  a  possible  means  of  igni- 
tion of  nebula?.  Our  first  discovery  of  nebulae  disclosed 
them  existing  already  at  an  intense  temperature.  Again 
and  again  the  question  has  been  raised,  "Whence  the 
heat?"  We  could  only  reply,  "That  is  a  mystery.  The 
•incandescent  condition  may  be  primordial.  Who  knows 
but  matter  may  be  created  incandescent  ?  "  Such  answers 
and  such  suggestions  have  been  offered.  Now,  in  accord- 
ance with  the  theory  of  nebular  conglomeration,  we  may, 
if  we  please,  recognize  the  possibility  of  the  creation  —  or 
at  least,  the  normal  existence  —  of  matter  in  any  assigna- 
ble state;  but  we  have  grounds  for  tracing  nebular  history 
one  step  farther  back.  We  must  conceive  of  dark  nebulae 
that  have  not  yet  been  pounded  into  a  white  heat.  We 
must  conceive  of  nebulous  particles  now  first  marshalling 
raw  recruits  of  matter  into  a  forming  phalanx.  Even  yet, 
the  mystery  of  beginnings  hangs  over  us.  We  have  not 

*  These  sentences  were  written  before  the  arrival  of  Nature  of  January  10, 
1878,  where  a  communication  of  James  Croll  sets  forth  an  identical  suggestion. 
On  the  heat  generated  by  the  impact  of  cosmical  bodies  see  also  Croll :  Climate 
and  Time,  p.  353.  Two  bodies  each  half  the  mass  of  the  sun  moving  directly 
toward  each  other  with  the  velocity  of  476  miles  a  second,  would  by  their  con- 
cussion generate  in  a  single  moment  heat  sufficient  to  last  50,000,000  years  at  the 
present  rate  of  solar  radiation. 


94  NEBULAR    LIFE. 

yet  seen  molecules  rolling  themselves  up  into  visibility. 
We  have  never,  even  in  imagination,  seen  atoms  emerging 
from  the  dread  abyss  of  nothingness.  Let  us  explain  all 
we  may;  let  us  seek  out  all  antecedent  conditions  possi- 
ble, enough  will  still  remain  to  pique  our  curiosity,  and 
awe  us  by  its  mystery.  Nay,  the  farther  we  trace  the 
links  of  the  chain  of  causation,  the  more  palpably  we  feel 
the  need  of  some  support  which  is  not  one  of  the  links  in 
the  chain,  but  is  superior  to  the  principle  of  finite  causa- 
tion, and  is  self-sufficient,  existing  out  of  relation  to  suc- 
cession, time  and  space. 

g2.     NEBULAR  ROTATION. 

1.  Causes  of  Rotation. —  It  thus  appears  that  the 
hypothesis  of  nebular  conglomeration  explains  two  other- 
wise inexplicable  phenomena  —  nebular  amorphism  and 
nebular  heat.  A  third  phenomenon,  hitherto  mysterious 
and  unexplained,  is  equally  accounted  for.  That  is,  the 
rotary  motion  which  sometimes  arises  in  nebulous  masses. 
This  difficulty  has  often  balked  belief  in  the  nebular  theory 
of  the  origin  of  the  solar  system.*  The  moment,  however, 
that  we  recognize  the  probability  of  the  collision  of  nebu- 
lar masses,  the  idea  of  rotation  necessarily  arises.  A 
nebular  mass  comparatively  minute,  impinging  upon  a 
mass  of  any  dimensions,  would  inevitably  generate  a  rota- 
tion, in  every  case  except  when  the  centres  of  gravity  of 
the  two  masses  moved  toward  the  same  point,  and  (unless 
moving  in  the  same  staight  line)  with  such  velocities  as  to 
reach  it  at  the  same  instant.  This  is  a  case  which  is  im- 

*Rev.  W.  B.  Slaughter  says:  "It  is  to  be  regretted  that  the  advocates  of 
this  [nebular]  theory  have  not  entered  more  largely  into  the  discussion  of  it 
[the  origin  of  rotary  motion].  No  one  condescends  to  givo  us  the  rationale  of  it. 
How  does  the  process  of  cooling  and  contracting  the  mass  impart  to  it  a  rotary 
motion?"  (The  Modern  Genesis,  p.  48.)  Even  Hclmholtz  says  the  rotation 
"must  be  assumed."  (Interaction  of  Natural  Forces,  Youman's  ed.,  231; 
Popular  Scientific  Lectures,  175.) 


NEBULAR    ROTATION. 


95 


possible  in  the  ratio  of  millions  to  one.  I  have  heretofore 
stated  that  when  the  two  bodies  consist  of  matter  as  dense 
as  the  earth  and  a  cold  meteorite  descending  from  a  distance* 
of  a  hundred  thousand  miles,  the  small  body  would  proba- 
bly be  so  much  deflected  by  lateral  attractions  as  to  miss 
the  large  one,  and  would,  consequently,  begin  to  revolve 
about  it  in  an  orbit  more  or  less  elliptical.  With  masses 
of  matter  as  voluminous  as  nebulae,  such  orbital  revolu- 
tions must  sometimes  be  established  ;  but  it  is  very  appar- 
ent that  the  collision  is  vastly  more  probable  than  in  the 
case  of  smaller  and  denser  masses.  Rotation,  conse- 
quently, would  be  the  general  condition  of 
nebular  masses. 

Now,  let  us  consider  the  two  general 
cases  which  would  arise  in  the  impact  of 
nebula  against  nebula. 

(1.)  FIRST  CASE. — The  centres  of  gravi- 
ty of  two  nebulce  move  toward  one  point 
with  such  velocities  as  to  reach  it  simul- 
taneously. We  recognize  at  least  two 
sub-cases. 

(a)  When  the  centres  of  gravity  move 
along  one  straight  line.  Here  in  the  pos- 
sible case  in  which  no  rotation  would 
ensue,  the  resultant  nebula,  in  addition  to 
a  distorted  form,  would  simply  experience 
an  altered  motion  of  translation  in  space. 
If  three  nebula?,  A,  B  and  C,  (Figure  19) 
lie  with  their  centres  of  gravity  in  one 
straight  line,  each  centre  of  gravity  is 
drawn  toward  each  of  the  others  with  a 

force  proportional  to  the  masses  and  the 

FIGURE    19.     Mo- 
mverse  squares  of  the  distances.     At  the       TION  OF  THREE 

end  of  a  certain  time,  B  would  be  drawn  by       NEBULA   IN 
the  attraction  of  A  to  b,  and  by  the  attrac-       SUB-CASE  a. 


96  NEBULAE    LIFE. 

tion  of  C,  to  b' .  C  would  be  drawn  by  the  attraction  of 
A  to  cy  and  by  the  attraction  of  B  to  c' .  A  would  be 
'drawn  by  the  attraction  of  B  to  a,  and  by  the  attraction 
of  C  to  a.2 ;  its  resultant  place  would  be,  therefore,  at  a'. 
The  new  positions  are  therefore  b' ,  c'  and  a'.  A  has 
made  some  movement  toward  B,  but  C  has  made  more  in 
the  same  direction.  C  is  therefore  approaching  A,  and 
will  eventually  join  A,  and  coalesce  with  it.  The  virtual 
motion  of  A  in  the  direction  of  C  will  therefore  cease, 
and  A  will  move  toward  B  with  a  velocity  increased  by 
the  amount  by  which  C's  former  attraction  drew  A  toward 
C.  That  is,  the  translation  of  A  through  space  will  be 
augmented  by  the  impact. 

(b)  The  second  sub-case  is  when  the  centres  of  gravity 
do  not  move  along  one  straight  line.  Here  A  (Figure  20) 

is  attracted  by  B  and  C, 
and  the  resultant  of  the 
two  attractions  brings  A 
to  a.  Similarly,  B  is  at- 
tracted by  A  and  C,  and 
takes  a  course  between 
the  two  attractions  to  a. 
Finally,  C  is  attracted  by 
A  and  B,  and  arrives  at 
«  at  the  same  instant 
FIGURE  20.  MOTION  OP  THREE  NEBULA  when,  by  hypothesis,  A 
IN  SPACE.  CASE  I,  SUB-CASE  b. 

and  B  arrive  at  the  same 

point.  It  is  evident  that  there  will  be  no  tangential  re- 
sultant, and  no  rotation  will  ensue;  but  the  united  mass 
will  undergo  a  translation  in  space,  in  the  direction  of  the 
resultant  of  three  momenta. 

(2.)  SECOND  CASE. — The  centres  of  gravity  move  toward 
a  common  point  with  such  velocities  as  to  pass  it  succes- 
sively. The  nebula  A  is  attracted  by  B  and  by  C  (Fig. 
21.  The  last  figure  also  illustrates  this  case,  supposing 


NEBULAR    ROTATION. 


97 


the  three  bodies  to  reach  a  successively).  B  is  also  at- 
tracted by  C,  but  owing  to  relative  positions  and  masses 
(as  we  may  assume)  is  less  affected  by  C  than  A  is.  A 
and  B  both  move  toward  «,  but  A  will  reach  the  point,  let 
us  suppose,  a  little  before  B.  It  will  be  struck  by  B 
therefore,  tangentially,  and  both  nebulous  masses,  at  least 
upon  their  exterior,  will  acquire  a  rotation  in  the  same 
direction.  If  the 
deflecting  force  ex- 
erted by  C  is  such 
that  A  and  B  ap- 
proach each  other 
to  a  distance  but 
little  less  than  the 
sum  of  their  radii, 
they  will  not  co- 
alesce unless  their 
velocities  are  low, 
but  will  each  ac- 
quire a  rotary  mo- 
tion, and  each  pass 
on  maintaining  a 
separate  existence. 
But  if  their  cen- 
tres of  gravity  ap- 
proach within  a 
distance  sufficient- 
ly less  than  the  sum  of  their  radii,  the  two  nebulae  will 
coalesce.  Until  completely  coalesced,  they  will  present 
the  form  of  a  dumb-bell,  and  afterward,  of  an  irregular 
spiral,  whose  irregularity  will  continually  diminish  as 
the  coalescence  proceeds.  In  this  way,  forms  like  H 
1,173  and  H  1,622  (Fig.  8)  would  be  evolved. 

It  is  quite  conceivable  that  nebular  rotation  might  be 
generated  by  attraction,  in  cases  where  no  actual  impact 
7 


FIG  21.     MOTION  OF  THREE  NEBULAS  IN  SPACE. 
CASE  II. 


98 


NEBULAR   LIFE. 


takes  place.  Suppose  an  amorphous  nebula  A  (Fig.  22)  to 
be  so  situated  in  respect  to  B,  that  its  longer  diameter 
a  b,  makes  an  oblique  angle  with  the  line  A  B,  joining  the 
centres  of  gravity  of  the  two  nebulae.  One  extremity  of 
the  mass,  as  at  b,  will  experience  a  greater  relative  attrac- 
tion toward  B  than  the  other  extremity  of  the  mass  will 

experience;  and  this 
inequality  will  con- 
tinue as  long  as  the 
angle  B  A  b  is  not  a 
right  angle,  and,  in 
the  case  supposed,  as 
long  as  B  A  b  is  less 
than  a  right  angle. 
The  effect  must  be  to 
turn  the  nebula  A  in 
such  direction  that  its 
longer  diameter  pro- 
duced will  tend  to 
pass  through  the  cen- 
tre of  gravity  of  B. 
But  in  the  meantime, 
B  and  A  may  have 
travelled  to  widely 
separated  regions  of 
space.  The  rotation 
begun  in  A  will  there- 
fore continue  unhin- 
dered. It  will  continue  in  any  case  where  the  hindering 
action  of  B  is  less  than  the  action  which  inaugurated  the 
rotation;  as  for  instance  when  the  form  of  A  becomes 
more  symmetrical,  though  the  action  of  B  should  be 
reversed  by  change  of  position,  without  being  less.* 


FIQ  22.    ROTATION  RESULTING  WITHOUT 
ACTUAL  IMPACT. 


*  A  modern  writer  of  much  sagacity  has  maintained  that  an  amorphous 
nebula  would  be  made  to  rotate  by  the  tangential  action  of  currents  of  nebulous 


NEBULAR    ROTATION.  99 

2.  Causes  of  Nebular  Forms. — As  to  the  spiral  form 
of  nebula?  different  suggestions  may  be  made.  We  may, 
for  instance,  conceive  it  as  arising  from  the  action  of  a 
resisting  medium  in  space.  This  would  develop  a  retarda- 
tion in  the  peripheral  portions,  and  would  explain  the 
tendency  of  parts  to  be  left  behind,  as  indicated  in  certain 
features  of  spiral  nebul;e.  Other  phenomena  would  be 
explained  on  the  supposition  of  some  translation  through 
a  resisting  medium.  The  unequal  actions  resulting  from 
a  non-homogeneous  constitution  of  the  nebula  would  favor 
the  production  of  a  spiral  form. 

Professor  Daniel  Kirkwood  has  offered  the  following 
suggestion  on  this  subject:  "The  tendency  in  a  rotating 
nebula,  to  unequal  angular  velocities,  resulting  from  the 
increased  rapidity  of  condensation  from  the  equator  to- 
ward the  centre,  may  perhaps  also  account  for  the  phenom- 
ena of  spiral  nebuke.  If,  in  a  contracting  mass  of  vapor, 
a  free  motion  of  the  particles  among  themselves  be 
established  before  the  centrifugal  force  becomes  equal  to 
the  centripetal,  a  spiral  convergence  like  that  of  51  in 
Messier's  Catalogue  would  naturally  ensue."*  As  the 
motion  among  the  particles  can  never  be  perfectly  "  free," 
it  is  questionable  whether  the  result  would  not  be  a  strati- 
fied nebula,  rather  than  a  spiral  one.  The  only  probable 
cause  of  a  descent  of  particles  toward  the  centre  would  be 
their  superior  inherent  density.  These,  carrying  with 
them  the  higher  linear  velocity  of  the  exterior,  would  tend 
to  run  ahead  of  the  particles  whose  original  position  was 

matter  descending  from  higher  to  lower  levels  simply  by  the  action  of  the  central 
gravity  of  the  mass  (Jacob  Ennis:  The  Origin  of  (he  Stars,  221  seq.).  It  is,  how- 
ever, a  fundamental  principle  in  physics  that  no  rotation  could  be  generated  in 
such  a  mass  by  the  action  of  its  own  parts.  As  well  attempt  to  change  the 
course  of  a  steamer  by  pulling  at  the  deck-railing.  The  same  author  suggests, 
however,  that  the  attraction  of  neighboring  nebulae  would  contribute  to  the 
formation  of  surface  currents;  and  he  even  suggests  the  origination  of  rotary 
movements  by  nebular  impact. 

*  D.  Kirkwood,  Amer.  Jour.  Sci.,  II,  xxxix,  68,  Jan.  1865. 


100  NEBULAR   LIFE. 

less  exterior.  Now  friction  would  tend  to  equalize  these 
motions,  but  as  we  may  admit  that  this  result  would  not 
be  accomplished  instantly  at  each  stage  of  their  progress, 
we  must  conceive  a  spiral  motion  of  such  particles.  But 
there  seems  to  be  no  probability  that  the  relative  number 
of  such  particles  would  be  so  great  as  to  impart  a  con- 
spicuous spiral  structure  to  the  whole  central  mass.  And 
if  it  should,  to  what  could  it  amount?  The  motion  is  from 
all  sides  spirally  toward  the  centre;  the  possible  amount  of 
it  is  therefore  limited.  The  permanent  condition  of  the 
interior  would  be  either  rotation  in  annuli  or  rotation  with 
the  same  angular  velocity  as  the  exterior.  Evidently,  the 
progressive  acceleration  of  motion  in  these  nebulas  must 
be  from  the  centre,  not  toward  it  —  unless  the  form  results 
from  retardation  peripherally,  as  I  have  suggested. 

As  to  the  general  internal  mass,  aside  from  the  descent 
of  particles,  as  supposed,  it  rotates  with  the  same  angular 
velocity  as  the  exterior,  and  in  the  progress  of  contraction 
it  undergoes  acceleration  in  the  same  proportion  as  the 
exterior.  I  think  the  case  may  be  pushed  further.  The 
process  of  contraction  would  shorten  the  radius  of  revolu- 
tion of  exterior  particles  a  greater  amount  than  the  radius 
of  interior  particles;  and  hence  the  external  parts  would 
be  more  accelerated  than  the  internal;  and  the  internal 
would  rotate  with  less,  instead  of  greater  relative  angular 
velocity.*  It  is  true  that  a  given  amount  of  radius- 
shortening  in  the  exterior  parts  would  cause  less  accelera- 
tion of  angular  velocity  than  the  same  amount  of  short- 
ening in  the  internal  parts,  since  the  angular  velocity 
varies  inversely  as  the  square  of  the  radius;  but  in  a 
rogular  process  of  shrinkage  the  radius  of  revolution  of 
the  external  particles  would  be  shortened  by  an  amount 
equal  to  the  sum  of  the  shortenings  of  the  radii  of  all  the 
particles  within  it;  and  this  would  give  the  external 

*  See,  further,  Part  II,  ch.  i,  §2,  2,  (2). 


NEBULAR    ROTATION.  101 

particles  a  much  greater  acceleration  than  the  internal. 
Though  this  is  not  the  nature  of  Professor  Kirkwood's 
reasoning,  we  may  inquire  whether  excess  of  angular 
velocity  in  the  external  parts  would  not  develop  a  spiral 
structure.  Of  course,  that  would  be  the  tendency,  and 
the  motion  would  not  reach  a  limit,  as  in  the  case  of 
internal  particles  moving  spirally  toward  the  centre.  The 
spiral  structure,  however,  would  be  reversed.  But  all  this 
peripheral  excess  of  motion  would  be  opposed  by  mutual 
friction  of  parts  and  by  the  resisting  medium.  Nor  is  it 
conceivable  that  the  slight  residual  excess  of  peripheral 
motion  should  develop  so  strong  a  tendency  to  diverge 
tangentially  from  the  general  centre  of  gravity  as  is  mani- 
fest in  actual  spiral  nebulse.  The  spiral  structure  would 
be  close  and  entirely  inconspicuous. 

Professor  G.  A.  Hinrichs  thinks  the  spiral  form  must 
result,  in  a  large  nebula  of  greatly  excessive  internal  den- 
sity, from  the  excessive  rotary  velocity  of  the  interior 
portions.*  This  conception  is  perhaps  not  distinct  from 
the  last;  and  the  same  comments  may  be  made  upon  it. 
Furthermore,  it  implies  —  what  may  not  generally  be 
true  —  that  the  central  density  was  acquired  after  rotation 
began;  and  it  must  be  confessed  that  rotation  is  likely 
to  be  an  early  incident  of  nebular  life,  and  much  aggrega- 
tion of  matter  is  likely  to  follow.  But  it  may  be  further 
said  that  this  central  acceleration,  should  it  become  a  fact, 
would  seem  to  be  a  process  most  likely  to  arise  in  an 
advanced  stage  of  the  nebula,  when  the  symmetry  of  out- 
line would  not,  by  the  mere  reaction  of  internal  rotation, 
develop  those  patchy  forms  which  characterize  many  of 
the  spiral  nebulse.  The  spiral  form  is  primitive.  It  is  not 
a  form  of  equilibrium;  it  tends  to  settle  into  the  oblate 
spheroid;  and  this  is  the  form  to  be  expected  after  nebu- 
lar life  has  advanced  far  enough  to  develop,  if  it  were 

*  G.  A.  Hinrichs,  Amer.  Jour.  Science,  II,  xxxix,  141-3. 


102  NEBULAR   LIFE. 

physically  possible,  any  excessive  internal  rotation.  Fi- 
nally, any  spiral  arrangement  resulting  from  excess  of 
internal  rotation  would  be  closely  coiled,  approximating  a 
spheroid,  and  not  by  any  means  the  enormous  open  coils 
of  the  actual  nebulae  of  this  class. 

Mr.  Herbert  Spencer  has  conceived  that  a  multitude  of 
flocculent  nebular  masses  descending  from  the  outer  por- 
tions of  an  extensive  nebula,  would  be  arranged  in  a  spiral 
manner;*  and  an  anonymous  writer  has  expressed  the 
opinion  that  the  simple  process  of  contraction  in  a  diffused 
nebulous  mass,  or  spiral  descent  of  its  constituent  parts, 
would  develop  a  spiral  form.f 

A  nebula  shaped  like  a  sickle  presents  the  appearance 
of  a  nebulous  body  moving  in  an  orbit  through  a  resisting 
medium.  The  resisting  medium  is  probably  a  fact.  The 
orbital  motion  would  be  attributable  to  two  forces  —  one 
an  impulse  exerted  tangentially,  and  the  other  a  constant 
force  exerted  centrally.  The  tangential  force  it  is  not 
difficult  to  conceive  as  existing.  A  central  force,  indeed, 
is  exerted  by  every  cosmical  mass  of  matter;  but  a  central 
force  ruling  the  orbital  movement  of  an  external  body 
must  contain  a  large  mass  relatively  to  the  moving  body. 
The  central  body  should,  therefore,  be  as  visible  as  the 
body  moving  around  it.J  Now  when  we  contemplate  the 
sickle-shaped  nebula  H.  3,239  (Figure  7),  we  detect  evi- 
dences of  the  orbital  motion  of  a  body,  but  do  not  dis- 
cover the  body  which  could  serve  as  its  centre  of  motion. 
We  might  conjecture  that  such  body  has  not  yet  become 
luminous;  but  even  then,  the  orbit  of  the  revolving  body 
is  so  small  relatively  to  its  volume,  that  we  can  hardly 
suppose  a  body  of  sufficient  mass  could  be  contained 

*  Spencer,  Westminster  Review,  Ixx,  114,  July,  1858. 

^rNorth  American  Review,  xcix,  26,  July,  1864. 

Jin  any  cage,  it  will  be  remembered,  whatever  the  relative  sizes  of  the  two 
bodies,  each  really  revolves  around  the  common  centre  of  gravity  between 
them. 


NEBULAR    ROTATION".  103 


within  it.  The  con- 
ception of  an  orbital 
motion  as  the  cause 
of  the  sickle  form  pre- 
sents difficulties  which 
we  must  try  to  escape 
by  some  different  sup- 
position. 

Let  us  assume  a 
considerable  mass  mov- 
ing in  the  direction 
from  B  to  C,  Figure 
23.  A  nebulous  mass 
located  at  A,  would 
be  drawn  at  first  in 
the  direction  A  B.  If 
it  moved  in  a  resisting 
medium  it  would  be- 
come somewhat  elon- 
gated in  that  direction 
—  the  lightest  parti- 
cles being  kept  behind. 
When  the  attracting 
body  had  reached  «' 
the  nebula  would  be 
drawn  toward  that 
point — its  direction 
being  slightly  changed. 
So,  as  the  attracting 
body  reached  the  points 
«„  «„  «4,  «5,  ««,  «T  and 
C,  the  nebula  would 
be  drawn  successively 

FIG.  23.     POSSIBLE  ORIGIN  or 

THE  FALCATE  FORM 

or  NEBULA. 


104  NEBULAR   LIFE. 

toward  those  points.  That  is,  it  would  move  in  a  curve 
with  a  radius  continually  diminishing,  as  long  as  the  at- 
tracting body  should  continue  to  approach;  but  with  a 
radius  gradually  increasing  again,  after  the  attracting 
body  should  begin  to  recede.  In  other  words,  the  path  of 
the  nebula  would  be  a  curve  with  two  branches  somewhat 
symmetrical  with  respect  to  each  other. 

It  ought  perhaps  to  be  said  that  the  attracting  body 
feeling  the  reciprocal  influence  of  the  nebula,  would  not 
move  along  the  straight  line  B  C,  but  along  the  hyperbola 
B'  D  E. 

The  gyratory  motion  of  a  nebula  which  is  not  homo- 
geneous would  result,  in  a  resisting  medium,  as  I  have 
already  indicated,  in  a  spiral  form.  But,  if  the  nebula 
should  slowly  assume  a  homogeneous  character,  having 
similar  density  throughout  each  concentric  zone,  the  spiral 
would  be  gradually  succeeded  by  a  rotating  spheroid.  A 
nebulous  mass  homogeneous  from  the  beginning,  and  sym- 
metrical in  form,  would  probably  never  assume  the  form  of 
a  spiral.  One  appointed  form  then,  of  all  rotating  nebula?, 
is  that  of  a  spheroid. 

3.  Influence  of  Resisting  Medium. — One  suggestion 
which  may  be  of  importance  in  a  subsequent  discussion, 
remains  to  be  made.  If  a  resisting  medium  act  on  the 
motions  of  nebulous  masses  in  space,  it  would  not  only 
induce  a  spiral  form  in  a  non-homogeneous  rotating  nebula, 
but  in  a  homogeneous  one  would  slowly  establish  a  rela- 
tive retrograde  movement  of  the  superficial  portions. 
This,  by  friction  with  the  deeper  portions,  would  tend  to 
retard  their  rotary  motion,  and  thus,  as  a  final  consequence, 
the  total  rotary  motion  would  be  retarded.  The  actual 
velocity  of  rotation  would  never  be,  therefore,  in  a  nebula 
continuing  to  condense  after  rotation  had  begun,  as  rapid 
as  would  be  demanded  by  the  shortened  radius  of  the  ro- 
tating spheroid.  It  may  be  further  said  that  the  estab- 
lishment of  a  retarding  superficial  current  would  not 


NEBULAR    ROTATION.  105 

necessarily  be  restricted  to  nebulae  of  uniform  density. 
Whenever  the  nebulous  matter  should  have  become  some- 
what closely  and  uniformly  gathered  together  within  a 
certain  space,  the  included  portions  of  the  resisting  medium 
would  partake  of  the  gyratory  motion  of  the  nebula,  and 
the  superior  power  of  a  denser  interior  to  overcome  ethereal 
resistance  would  have  no  opportunity  to  exert  itself. 
Hence  a  gradually  increasing  internal  density  would  not 
affect  the  formation  of  retarding  superficial  currents  in  a 
nebula  in  this  sense  non-homogeneous. 

Whether  rotating  or  stationary,  every  nebula  is  con- 
tinually wasting  its  heat.  The  process  of  refrigeration  is 
probably  retarded  by  the  frequent  impact  of  new  accessions 
of  matter.  Inevitably,  however,  the  nebula  must,  in  the 
progress  of  ages,  become  reduced  in  temperature. 

4.  Nebular  Evolution  without  Rotation. — In  a  non- 
rotating  nebula,  especially  if 
possessing  an  irregular  and  ex- 
tremely flattened  shape,  we  may 
contemplate,  besides  the  general 
centre  of  gravity,  the  centres  of 
gravity  of  its  different  portions. 
Under  certain  conditions  in  the 
course  of  cooling  and  shrinkage, 
a  nebula  may  break  up  into  FIG.  34. 

numerous    pieces    by    a    process  COAGULATING  NEBULA,  OB 

"CURDLING  FIRE-MIST." 
analogous  to  a  coagulation  and 

withdrawal  of  part  from  part  (Figure  24),  as  is  daily  illus- 
trated in  the  patchy  arrangement  of  the  aqueous  vapors 
which  float  in  our  atmosphere.*  Under  other  condi- 

*  Of  a  certain  portion  of  the  nebula  in  Orion,  the  so-called  Huygcnian  region, 
Sir  John  Herschel  writes  as  follows:  "I  know  not  how  to  describe  it  better  than 
by  comparing  it  to  a  curdling  liquid,  or  a  surface  strewed  over  with  flocks  of 
wool,  or  to  the  breaking  up  of  a  'mackerel'  sky  when  the  clouds  of  which  it 
consists  begin  to  assume  a  cirrous  appearance.  It  is  not  very  unlike  the  mot- 
tling of  the  sun's  disk,  only  (if  I  may  so  express  myself)  the  grain  is  much 


106 


NEBULAR    LIFE. 


tions,  as  we  may  reasonably  suppose,  liquefied  molecules 
may  gather  about  numerous  partial  centres  of  gravity 
(Figure  25),  as  was  first  sug- 
gested by  Sir  William  Her- 
schel.  In  either  case,  as  the 
cooling  should  proceed,  a 
cluster  of  luminous  bodies 
would  come  into  existence, 
which  would  present  the  ap- 
pearance of  a  resolvable 
nebula.  This  is,  perhaps,  a 


. 

rotating  nebulas. 
§  3.     NEBULAR  ANNULATION. 

1.  The  Law  of  Equal  Areas.  —  It  is  probable  that 
most  of  the  nebula?  have  rotary  motions.  It.  would  seem 
that  mutual  attractions,  if  not  actual  collisions,  must,  in 
the  great  majority  of  cases,  generate  rotations  in  one  or 
another  of  the  methods  already  indicated.  In  fact,  when 
we  contemplate  the  delicacy  of  the  adjustment  of  the 
forces  acting  on  a  tenuous  body  poised  in  distant  space, 
and  surrounded  by  millions  of  other  bodies,  all  changing 
perpetually  their  relative  distances  and  positions,  it  be- 
comes almost  incredible  that  a  resultant  should  not  arise, 
in  the  course  of  millions  of  years,  which  should  act,  how- 
ever faintly,  as  a  tangential  force.  Once  stirred  from 
a  rigid  attitude,  a  motion  is  initiated  which  must  change 
fundamentally  the  course  of  nebular  development.  Let 
us  consider  the  course  of  development  which  the  laws 
of  physics  necessitate,  when  a  rotation  has  been  inau- 

coarscr  and  the  intervals  darker;  and  the  flocculi,  instead  of  being  generally 
round,  are  drawn  into  little  wisps.  They  present,  however,  no  appearance  of 
being  composed  of  small  stars,  and  their  aspect  is  altogether  different  from  re- 
tollable  nebula:."  (Memoirs  of  the  Astronomical  Society  of  London,  vol.  ii.) 


NEBULAR   ANNULATION".  107 

gurated  in  a  mass  of  highly  heated  vapor  suspended  in 


No  proof  is  required  that  such  a  heated  body  would 
radiate  its  heat  into  surrounding  colder  space.  No  proof 
is  required  that  it  would  coincidently  contract.  To  sup- 
pose otherwise  would  be  to  assume  an  order  of  nature 
different  from  that  which  all  induction  has  established; 
and  this  would  bring  to  a  summary  end  all  reasoning  on 
physical  subjects.  But  a  shrinkage  in  the  volume  of  a 
rotating  nebula  would  necessitate  an  acceleration  of  its 
rotation.  By  a  mathematical  principle  of  physics,  known 
as  "the  law  of  equal  areas  in  equal  times,"  the  sum  of 
the  products  of  the  particles  of  a  rotating  vapor  into  the 
areas  described  by  their  radii  vectorcs  projected  on  the 
plane  of  the  equator,  is  always,  in  the  same  body,  a  con- 
stant quantity.  In  other  words,  each  radius  vector 
describes  the  same  area,  whether  its  length  be  increased 
or  diminished;  and  hence,  if  its  length  is  diminished  its 
angular  velocity  must  be  increased  to  enable  it  to  sweep 
over  the  same  area  in  the  same  time.  This  principle,  thus 
enunciated,  may  not  be  quite  clear  to  some  of  my  readers, 
and  I  will  endeavor  at  least  to  render  intelligible  the 
meaning  of  the  proposition,  though  its  proof  could  not  be 
presented  without  resort  to  mathematical  operations. 

Let  us  suppose  that  in  Figure  26  the  circle  ABC 
represents  a  section  through  a  rotating  sphere  of  heated 
vapor,  in  the  plane  of  its  equator.  The  circumference 
ABC  is,  therefore,  the  equator,  and  it  may  be  conceived 
as  represented  by  a  series  of  particles  linearly  arranged. 
Let  one  of  these  particles  be  at  #,  then  a  O,  drawn  from 
it  to  the  centre  of  the  circle,  is  its  radius  vector.  If,  in 
the  progress  of  rotation,  the  particle  a  is  transported  to 
b,  its  radius  vector  will  sweep  over  the  space  between  O  a 
and  O  b.  But  suppose  that  in  the  course  of  time,  cooling 
has  contracted  the  sphere  to  such  extent  that  when  the 


108 


NEBULAR  LIFE. 


FGI.  26.    THE  "  LAW  OF  EQUAL  AREAS," 


same  molecule  ar- 
rives in  the  same 
angular  position  as 
before,  it  is  not  at 
a,  but  at  a'.  Its 
radius  vector  is  now 
O  a' ,  a  certain 
amount  shorter  than 
before,  and  if  it 
sweeps  forward  with 
the  same  velocity  as 
before,  it  will  not 
sweep  over  the  same 
area  in  the  same 
time  as  before.  It 

must,  therefore,  move  more  rapidly,  so  that  in  the  same 
time  which  formerly  carried  it  from  a  to  b,  it  will  now  be 
carried  from  a'  to  b' ,  making  the  area  a'O  b'  equal  l,o  the 
area  a  O  b.  If  these  statements  are  true  of  one  particle 
in  the  circumference  of  A  B  C,  they  must  be  true  of  all  the 
particles  in  that  circumference.  But  immediately  within 
this  circumference  we  may  conceive  another,  the  particles 
of  which  are  moved  in  every  respect  exactly  like  those  in 
the  circumference  ABC,  except  that  their  absolute  veloc- 
ity is  less  all  the  time.  As  the  sphere  contracts,  these  par- 
ticles also  will  move  with  accelerated  velocity.  But  within 
the  last  named  circumference  we  may  conceive  others, 
until  the  whole  area  inclosed  within  A  B  C  is  seen  made 
up  of  a  series  of  concentric  circles  of  particles,  each  par- 
ticle rotating  according  to  the  same  law  as  the  particle 
at  a.  Next,  we  may  easily  conceive  that  another  sheet  of 
particles  is  immediately  contiguous  to  this  one  on  each 
side.  The  motions  of  its  particles,  it  will  readily  be  under- 
stood, are  controlled  by  the  same  law  of  equal  areas.  It 
follows  that  the  rotation  of  the  whole  sphere,  which  is 


NEBULAR   ANNULATION".  109 

made  up  of  parallel  sheets  of  particles,  must  be  accelerated 
in  the  same  manner  as  the  particle  at  «,  during  a  process 
of  cooling  and  contraction  of  the  mass.* 

The  same  conclusion  may  be  reached  from  the  principle 
that  the  angular  velocities  of  two  rotating  spheroids  hav- 
ing the  same  mass  and  the  same  angular  momentum,  but 
of  different  equatorial  diameters,  are  to  each  other  inversely 
as  the  squares  of  their  radii  of  gyration. f  The  radius 
of  gyration  is  the  distance  from  the  axis  of  rotation  to 
the  centre  of  gyration,  or  point  within  the  mass  at  which 
we  can  conceive  an  opposing  force  applied  which  would 
completely  arrest  the  rotation  without  jarring  or  wrench- 
ing the  axis. 

Not  only  is  the  angular  velocity  increased,  but  the 
actual  velocity  of  the  periphery  also;  and  it  is  chiefly  the 
increase  of  the  actual  velocity  which  increases  the  cen- 
trifugal force  of  a  particle.  Some  critics  fall  under  the 
misapprehension  of  considering  only  angular  velocity.:}: 
That  contraction  increases  the  actual  as  well  as  the  angular 
velocity  is  obvious  from  the  simple  consideration  that  the 
centrifugal  force  of  a  particle  at  the  equator  is  measured 
by  the  square  of  the  actual  velocity  divided  by  the  radius 

*In  this  explanation,  the  particles,  for  the  sake  of  simplicity,  are  assumed 
to  be  ail  of  the  same  mass.  Thus  under  the  principles'  enunciated,  they  become 
a  common  factor  which  may  be  cancelled. 

t  The  angular  momentum  of  a  spheroid  whose  mass  is  M,  axis  of  gyration,  k, 
and  angular  velocity,  9,  is 

M**e. 

Supposing  the  same  mass  to  have  contracted  till  its  axis  of  gyration  ia  k' 
and  the 'angular  velocity  6',  it*  angular  momentum  will  be  expressed  by 
MW. 

But  as  the  angular  momentum  remains  constant,  we  have 


whence  6:6'-.:  h™  :  &. 

And  for  a  particle  in  the  periphery,  k  and  k'  equal  the  radii  vectores  r  and  r' 
In  the  two  positions,  and  we  get 

6:  6>::r'*  :  r", 

That  is,  the  angular  velocity  increases  as  the  square  of  the  radius  vector  of 
the  particle  diminishes. 

$Rev.  W.  B.  Slaughter:     Tfie  Modern  Genesis,  pp.  85-87. 


110  NEBULAR   LIFE. 

of  the  equator.  Since,  therefore,  the  radius  is  continually 
diminishing,  the  actual  velocity  is  continually  increasing.* 

2.  Abandonment  of  a  Ring. — Let  it  be  granted  then, 
that  the  process  of  necessary  cooling  and  contraction 
would  be  accompanied  by  an  accelerated  rotation.  This 
would  be  accompanied,  in  turn,  by  an  increased  oblateness 
at  the  extremities  of  the  axis.  As  soon  as  rotation  begins, 
the  momentum  of  the  particles  around  the  equator  is 
greater  than  that  of  particles  on  either  side,  and  it  con- 
tinually decreases  to  the  poles,  where  it  is  nothing.  The 
momentum  of  a  particle  measures  its  tendency  to  fly  off 
in  a  tangent  or  straight  line  in  the  direction  in  which  the 
particle  is  moving  at  any  instant.  This  is  a  tendency 
which,  in  part,  draws  it  away  from  the  axis  around  which 
it  moves.  As  the  velocity  of  rotation  increases,  each  par- 
ticle must  therefore  experience  a  stronger  tendency  away 
from  the  axis  of  rotation.  As  this  centrifugal  tendency 
is  greatest  at  the  equator,  the  equatorial  parts  will  pro- 
trude, and,  if  there  is  any  mutual  attraction  among  the 
particles,  those  on  each  side  of  the  equator,  aided  by  cen- 
trifugal tendency,  will  flow  away  from  the  poles,  and  thus 
diminish  the  polar  diameter,  while  the  equatorial  is  in- 
creased. In  other  words,  the  sphere  will  become  an  oblate 
spheroid,  with  oblateness  increasing  in  proportion  as  the 
velocity  of  rotation  is  increased. 

What  must  this  process  end  in?  Evidently,  the  ob- 
lateness will  finally  reach  such  an  extent  that  the  equa- 

*  Letting  v  and  v'  represent  the  actual  velocities  of  a  particle,  m,  in  the  two 
situations,  before  and  after  a  certain  amount  of  contraction,  and  r  and  r' the 
two  corresponding  values  of  the  radius  vector,  the  centrifugal  force  in  the  two 

situations  will  be  ^-  and  ™-^—.  But  as  the  centrifugal  force  varies  directly 

as  the  centripetal  force,  that  is,  inversely  as  the  square  of  the  radius  vector,  we 
have 

«£!  •  ?L£?  ..  ,«  .  r, 

r  r' 

From  which  t'a  :  »'»  ::  r'  :  r, 

But  r  >  r7,  .•.  ?'"  >  ?'a  or  r'  >  v. 


NEBULAR   AXNULATIOH.  Ill 

torial  particles  will  have  a  centrifugal  tendency  equal  to 
the  centripetal.  Then,  if  any  further  contraction  of  the 
spheroid  takes  place,  the  equatorial  particles  will  not  fol- 
low, but  will  be  left  suspended  in  equilibrium  between  the 
two  tendencies.  An  entire  equatorial  ringlet  of  particles 
will  attain  this  equipoised  condition,  and  the  remainder  of 
the  mass  will  proceed  to  shrink  away  from  it.  (See  Fig- 
ure 27.) 

3.  Width  of  the  Ring. — Now,  if  we  could  neglect 
the  mutual  attractions  of  contiguous  particles,  it  is  ap- 
parent that  this  ringlet  would  be  extremely  narrow  and 
thin.  As  soon  as  detached  another  slender  ringlet  would 
separate  itself,  and  then  immediately  another,  and  so  on. 
The  series  of  slender  concentric  ringlets  thus  detached 
would  constitute  virtually  a  broad,  flat  and  thin  ring,  hav- 
ing a  slower  rate  of  rotation  on  its  outer  margin  than  on 
its  inner.  If  these  closely  contiguous  ringlets  should 
actually  coalesce,  the  friction  of  outer  and  inner  ones 
would  accelerate  the  outer  and  retard  the  inner  until  the 
angular  velocity  of  all  would  approach  uniformity.  But, 
disregarding  mutual  attraction  of  the  parts,  we  see  no 
cause  to  limit  the  process  by  which  slender  ringlets  would 
be  formed,  until  the  whole  mass  of  the  spheroid  should  be 
reduced  to  a  rotating  disc  essentially  continuous  from  cen- 
tre to  circumference.  But  here  two  suggestions  must  be 
made.  The  discoid  arrangement  would  be  but  a  momen- 
tary phase  in  each  concentric  ringlet,  because  (1),  when 
we  carry  the  conception  to  the  extent  indicated,  we  per- 
ceive that  disc-like  continuity  from  ringlet  to  ringlet  is  in- 
compatible with  the  physical  tendency  to  ever  increasing 
velocity  toward  the  centre  in  proportion  as  the  contraction 
is  actually  experienced  toward  the  centre.  (2)  Such  a 
disc  could  not  subsist  in  the  case  of  a  fluid  substance.  It 
would  gather  itself  into  a  single  ring.  The  transverse 
section  of  the  ring  would  be  ovate,  with  the  smaller  end 


112  NEBULAR   LIFE. 

turned  toward  the  axis  of  rotation.  Whatever  we  might 
conceive  to  result  from  unequal  velocities  in  a  flat  ring  of 
relatively  limited  extent,  it  is  evident  that  no  permanent 
disc-like  continuity  of  successively  equilibrated  matter 
could  ever  take  place  to  any  relatively  considerable  extent. 
Instead  of  a  broad  and  continuous  disc,  we  must  have  a 
series  of  concentric  rings  rotating  with  different  velocities. 
Nor  is  it  supposable  that  closely  approximated  ringlets, 
circumstanced  as  suggested,  would  perpetuate  their  com- 
mon existence  until  some  epoch  when  a  common  crisis 
should  simultaneously  change  the  condition  of  newer  and 
older  alike.* 

Undoubtedly,  mutual  attractions  of  contiguous  parti- 
cles and  masses  always  existed,  and  hence  we  have  no 
occasion  to  speculate  on  the  consequences  of  an  absence 
of  such  attractions.  If  then,  we  turn  back  in  thought  to 
the  epoch  when  the  first  equatorial  ringlet  of  particles 
should  have  been  left  detached  from  the  shrinking  re- 
mainder, we  perceive  that  the  next  inner  circle  of  particles 
must  be  actuated  by  a  centripetal  force  barely  sufficient  to 
overcome  the  centrifugal  tendency  experienced  in  that 
circle.  But  exterior  to  these  particles  is  the  ringlet  of 
particles  just  disengaged,  and  its  attraction  would  com- 
pletely neutralize  the  slight  excess  of  centripetal  force 
experienced  by  the  second  ringlet,  and  this  ringlet  would 
therefore  be  brought  into  a  state  of  equilibrium,  and 
would  also  be  left.  Now  the  third  ringlet  would  experi- 
ence a  stronger  predominance  of  centripetal  force,  but 
this  would  be  opposed  by  an  increased  attraction  exerted 
by  the  two  ringlets  exterior  to  it.  We  may  therefore 
conceive  that  a  third,  and  other  ringlets  would  almost 
simultaneously  become  detached.  How  broad  and  massive 

*  It  has  been  suggested  that  such  a  history  is  supposable.  See  D.  Kirk- 
wood,  Amer.Jour.  Scl.  II,  xxxviii,  5;  D.  Trowbridge,  id.  note;  S.  Newcomb: 
Popular  Astronomy,  497-8;  Du  Prel:  Die  Planetenbewohner,  6. 


NEBULAR    ANNULATIOX.  113 

the  aggregate  ring  would  be,  would  be  determined  by  the 
position  of  the  nascent  ringlet  at  which  the  centripetal 
force  should  exceed  the  centrifugal  force  (at  that  distance 
from  the  axis)  added  to  the  attraction  of  the  annular  mass 
exterior  to  it.  Now  every  successive  addition  which  may 
have  been  drawn  to  the  annular  mass  increases  its  distance 
from  the  next  ringlet  of  particles,  and  upon  this  its  influ- 
ence, though  increasing  with  the  growth  of  the  ring, 
diminishes  as  the  square  of  the  distance  increases.  Its 
influence,  that  is  its  contribution  to  the  centrifugal  ten- 
dency of  the  next  ringlet,  diminishes,  therefore,  more 
rapidly  than  the  centripetal  tendency  is  diminished  by  dim- 
inution of  the  residual  mass,  for  that  is  as  the  first  power 
of  the  mass;  and  it  increases  as  the  square  of  the  radius  of 
the  spheroid  is  diminished  by  contraction.  The  influence 
of  the  ring  diminishes  more  rapidly  than  the  joint  effect 
of  diminished  residual  mass  and  increased  rate  of  rotation. 
This  circle  of  equilibrium  would  determine,  therefore,  the 
line  of  separation  between  a  segregating  annular  mass 
and  the  residuum  of  the  spheroid.  In  other  words, 
an  annular  mass  of  relatively  considerable  amount 
would  separate,  and  a  secular  interval  would  intervene 
before  the  separation  of  another  annular  mass*  The 
condition  represented  by  Figure  27  may  therefore  be 
contemplated  as  one  of  the  primitive 
phases  of  a  rotating  nebula.  It  is 
observed  to  actually  exist  in  certain 
stellar  nebulae,  as  H  450. 

The  foregoing  exposition  assumes 
that  the  actions  concerned  would 
reach  their  resultant  somewhat  sim- 
ultaneously, and  the  ring  would  be 

**.  '      .  ,        .  .          FIG.  27.    NEBULA  IK  PRO- 

formed    without    any    considerably         CESS  OF  ANNULATION. 

*  Compare  D.  Trowbridge,  Amer.  Jour.  Sci.,  II.,  xxsviii,  35. 


114 


NEBULAR    LIFE. 


prolonged  period  of  growth.  The  influence  of  progressive 
contraction  of  the  nebula  is  therefore  neglected.  But 
contraction  would  proceed  during  whatever  period  might 
be  occupied  in  the  formation  of  the  ring.  We  may  con- 
sider, therefore,  what  would  result  on  the  assumption  that 
no  ringlet,  after  the  first,  would  leave  the  nebula  until 
entirely  equilibrated  between  centripetal  and  centrifugal 
tendencies.  This  assumption  depends  on  progressive  con- 
traction and  acceleration  for  the  successive  disengage- 
ment of  ringlets.  It  will  give  a  clearer  conception  of  the 


Fie.  28.    ILLUSTRATING  THE  DETERMINATION  or  THE  WIDTH  OF  A  NEBULOUS 
RING. 


conditions  limiting  and  determining  the  width  of  the  ring 
produced.  Let  ctb  (Figure  28)  represent  a  segment  of  a 
slender  ringlet  just  abandoned,  having  the  slight  interval 
a  &,  separating  it  from  the  new  periphery  of  the  nebula. 
Soon  the  peripheral  ringlet  k  I  will  attain  a  state  of  equi- 
librium. This  experiencing  a  positive  attraction  from  the 
ringlet  a  b,  and  no  tendency  to  fall  toward  the  centre  of 
the  nebular  mass,  must  move  toward  a  b.  The  external 
ringlet  becomes  thus  augmented  to  the  breadth  shown 


NEBULAR   ANNULATION.  115 

in  be,  and  the  interval  between  it  and  the  nebula  is  en- 
larged to  g  m.  Next,  another  ringlet  m  n  attains  a  state 
of  equilibrium,  and  will  similarly  be  drawn  to  b  c,  augment- 
ing the  external  ring  to  the  breadth  c  i  shown  in  c  d.  In 
due  time  the  ringlet  op  is  abandoned  and  drawn  to  c  d, 
augmenting  it  to  the  width  du  as  shown  at  d  e.  I  do  not 
conceive  the  actual  formation  of  distinct  ringlets  of  any  de- 
finable magnitude,  with  an  actually  periodic  passage  from 
the  periphery  of  the  nebula  to  the  growing  ring.  The 
abandonment  of  ringlets  is  momentary  and  continuous,  and 
the  passage  of  the  nebulous  matter  outward  is  in  the  nature 
of  a  continuous  flow  which  fills  the  intervening  space  with 
an  extremely  attenuated  nebulous  medium. 

At  length  the  breadth  of  the  growing  ring  becomes 
such  as  is  represented  at  ef,  and  the  interval  between  it 
and  the  nebula  has  widened  to  to  s.  Meantime  the  attrac- 
tion of  the  ring  exerted  upon  the  periphery  of  the  nebula 
has  been  continually  diminishing  as  the  square  of  the 
distance  increased.  It  has  become  diminished  to  such  an 
extent  as  to  be  comparatively  feeble.  A  differential  ring 
st,  feels  now  a  different  preponderance  of  forces.  The 
attraction  of  the  ring  does  not  cease  to  be  felt  to  some 
extent;  and  the  attraction  of  the  nebula  does  not  cease  to 
be  neutralized  by  the  centrifugal  tendency.  But  there 
have  all  along  been  two  actions  opposing  the  passage  of 
matter  to  the  ring  which  have  not  yet  been  mentioned. 
One  of  these  is  the  friction  of  the  ether  and  meteoroidal 
matter,  which  continually  retards  the  velocity  of  rotation, 
and  all  the  more  where  a  mass  as  thin  as  the  withdrawing 
ringlet  is  concerned.  This  diminishes  the  centrifugal  ten- 
dency, and  opposes  the  passage  outwards.  Besides  this, 
the  mutual  attraction  of  contiguous  parts  of  the  ringlet 
at  all  times  opposes  that  distension  implied  in  the  trans- 
formation to  a  ringlet  of  greater  circumference.  The  joint 
action  of  these  comparatively  minute  forces  determines 


116  XEBULAR    LIFE. 

a  critical  moment.  The  diminished  attraction  of  the  ring 
now  ceases  to  overcome  them.  A  ringlet  is  formed  at  st 
which  remains  unmoved  from  its  place.  It  constitutes  the 
starting  point  of  another  ring,  which,  in  turn,  goes  through 
a  similar  history.* 

Under  certain  conditions  the  growth  of  the  ring  would 
not  attain  its  limit  until  the  nebula  had  been  entirely  ex- 
hausted. The  nebula  would  be  thus  transformed  into  an 
annulus.  If  the  resistances  of  friction  and  the  mutual 
attraction  of  parts  of  the  ringlets  should  in  any  case  be 
inconsiderable,  the  attraction  of  the  ring  would  always 
preponderate  over  the  forces  opposed  to  the  translation  of 
matter  to  it,  and  the  growth  of  the  ring  would  be  indefi- 
nite.f 

It  does  not  seem  unreasonable  to  suppose  that  under 
certain  conditions,  as  for  instance,  an  extraordinarily  rare- 
fied condition  of  the  central  part,  the  centrifugal  tendency 
of  the  peripheral  parts  and  the  attraction  of  the  nascent 
ring  for  successively  more  interior  nascent  rings  should 
result  in  expanding  the  entire  mass  of  the  nebula  directly 
into  an  annulus.  This  tendency  once  inaugurated,  by  the 

*  Let  G'  =  attraction  of  the  ring  upon  the  nearest  point  of  the  nebula,  i.e. 
sum  of  the  components  (of  all  the  attractions  of  the  ring)  which  act  along  the 
shortest  line  from  the  point  to  the  ring. 

G  =  atttraction  of  nebula  upon  the  same  point. 
F  =  centrifugal  tendency  of  the  same. 
e  =  sum  of  frictional  resistances  to  its  motion. 
m  =  sum  of  mutual  attractions  opposing  separation  of  particles. 
Then,  as  long  as  we  have 

G'+F>G  +  «  +  m 
the  ring  will  continue  to  increase  in  breadth.    When 

G'+F  =  G  +  e  +  m 

the  ring  will  cease  to  receive  accessions  of  new  ringlets.  Thenceforward  we 
shall  always  have 


<  -. 

t  Since,  in  this  case,  e  -f  m  =  0,  and  by  hypothesis  G  =F  at  all  times  when 
onmilation  is  possible,  the  expression  G'-)-F>  G  -\-  e  -\-  m  reduces  to  G'  >  0, 
an  inequation  which  expresses  the  condition  of  ring-growth,  aiyl  will  continue 
true  until  e  -f  m  becomes  such  that  G'=  e  -f  m.  But  if  the  last  relation  is  never 
reached,  the  growth  of  the  ring  will  be  unlimited  as  long  as  the  nebula  is  unex- 


hausted 


KEBULAR   ANNULATION".  117 

vacation  of  the  central  region,  the  effect  of  further  con- 
traction would  be,  in  a  highly  tenuous  condition  of  the 
nebula,  to  enlarge  the  diameter  of  the  vacant  interior,  as 
well  as  to  diminish  the  outside  diameter  of  the  ring. 

A  tendency  of  this  kind  to  the  simple  annulus  is  by  no 
means  imaginary.  The  central  attraction  of  parts  near 
the  centre  would,  on  physical  principles,  be  slight,  since 
nearly  as  much  matter  would  lie  upon  the  side  toward  the 
periphery,  b,  Figure  29,  as  on  the  side  toward  the  centre, 
c.  At  the  centre  the  balance  of  tendencies  would  be  com- 
plete. The  periphery  and  the  centre 
would  therefore  be,  by  hypothesis, 
both  in  equilibrium.  The  periphery 
would  experience  no  tendency  to 
move  toward  the  centre.  The  cen- 
tral portions  would  experience  little 
or  no  tendency  to  remain  there. 
-Meantime  both  parts  attract  each 
other.  The  periphery,  with  progres- 
sive  shrinkage,  might  move  toward 

the  centre  until  accelerated  velocity  should  nullify  the 
attraction  of  the  central  portion.  The  latter  portion 
would  move,  by  its  own  gravity,  toward  the  periphery, 
until  a  state  of  condensation  should  be  reached,  such  as 
to  correspond  with  the  existing  temperature.  Thus,  I 
imagine,  a  simple  annular  nebula  might  originate,  such  as 
we  are  acquainted  with  in  the  Lyre  (Figure  11),  in  H 
1,909  and  H  2,621. 

Thus,  nebular  aggregation  and  secular  refrigeration 
may  reasonably  be  regarded  as  the  general  causes  of  the 
varied  forms,  conditions  and  evolutions  of  nebula?.  Let 
us  now  attempt  to  trace  the  development  some  steps 
farther. 

•Schellen:  Spectral  Analysis,  555  and  542,  Figures  192  and  193. 


118  NEBULAR   LIFE. 

4.  Non-annulating  Nebulce  and  Stratified  Rinc/s. — 
The  progressive  changes  of  nebula?  seem  to  be  toward  the 
stellar  condition.  Not  improbably,  many  nebula?,  espe- 
cially small  ones,  shrink  into  single  stars,  as  Sir  William 
Herschel  supposed.  Some  of  the  planetary  nebula?  may 
possibly  contract  indefinitely  without  breaking  into  separate 
nebulous  fragments.  In  either  event,  they  appear  to 
undergo  a  sort  of  annulation. 

It  seems  more  probable,  however,  that  most  nebula? 
break  up  normally  into  a  large  number  of  partial  masses. 
I  have  indicated  a  process  of  curdling  as  a  possible  step  in 
the  stellation  of  a  non-rotating  nebula.  Each  separate 
mass  may  be  regarded  as  embracing  in  some  instances, 
material  for  a  sun  and  planetary  system.  This  idea,  how- 
ever, supposes  that  a  rotation  comes  into  existence  in  each 
mass.  How  this  could  be  generated  while  the  physical 
conditions  are  such  as  to  favor  the  segregation  of  the 
masses,  and  thus  prevent  that  precipitation  of  mass  upon 
mass  which  is  the  most  obvious  cause  of  nebular  rotations, 
I  am  not  able  to  understand.*  I  must  leave  the  discrete, 
non-rotating  nebula,  if  such  really  exists,  for  the  further 
developments  of  science. 

As  to  rotating  nebula?,  I  have  shown  that  they  tend  to 
annulation.  A  ring  of  nebulous  matter,  if  little  disturbed 
by  external  perturbations,  may  rotate  indefinitely  around 
its  centre  of  gravity.  The  process  of  shrinkage  in  a 
persistent  rotating  ring  of  nebulous  or  pulverulent  matter 
would,  in  some  cases,  result  in  a  stratification,  or  sepa- 

*  I  formerly  regarded  nebular  collisions  as  many  times  the  most  probable 
cause  of  rotations;  but  later  reflection  leads  me  more  and  more  to  the  conviction 
that  simple  mutual  attractions  upon  amorphous  forms  suspended  in  space,  are 
competent  to  generate  universal  rotations.  It  becomes  more  and  more  apparent 
that  rotation  is  inevitable,  and  that  it  must  exist  even  in  the  planetary  and  curd- 
ling nebulae.  The  latter  are  resolvable  nebulue  which  nevertheless  give  a  spec- 
trum of  bright  lines,  and  hence,  must  consist  of  nebulous  matter  in  a  discrete 
condition.  Such  is  the  nebula  or  "cluster"  in  Hercules.  Even  the  separate 
i  of  a  curdling  nebula  must  sooner  or  later  rotate. 


SPHERATIOlsr   OP   RINGS. 


119 


ration  of  the  ring  into  two  or  many  concentric  rings 
(Figure  30).  The  stratified  condition  might  also  arise,  as 
Kant  first  suggested,  from  the  different  velocities  of  the 
outer  and  inner  portions  of  a  broad  ring  progressively 
disengaged.  It  is  also  quite  conceivable  that  every  annu- 
lar mass,  separated  after 
a  secular  interval,  should 
consist  originally  of  dif- 
ferential annuli  dropped 
off  in  small  consecutive 
elements  of  time.  These, 
if  ever  existing,  which  is 
not  probable,  must  nat- 
urally experience  a  strong 
tendency  to  coalescence  in 
groups,  at  the  same  time 
that  their  different  angu- 
lar velocities  might  resist 
the  coalescence  together 

of  rings  differing  much  in  diameter.  Be  the  cause  of 
stratification  what  it  may,  it  seems  to  be  at  least  an  oc- 
casional incident  of  nebular  life.  A  persistent  example  is 
actually  noted  in  the  rings  of  Saturn. 

§  4.    SPHERATION  OF  RINGS. 

1.  Disruption  of  a  Ring. — Sooner  or  later,  external 
perturbations  or  actual  collisions  must  generally  result  in 
the  breaking  up  of  a  nebulous  ring.  In  some  instances 
perturbation  would  develop  undulations  which,  continu- 
ally exaggerated,  would  finally  produce  rupture,  or  destroy 
the  equal  distribution  of  matter  around  the  ring.  An 
increase  of  mass  on  one  side,  however  caused,  would 
draw  still  other  matter  toward  it.  The  ring  on  the  oppo- 
site side  would  become  slender  (Figure  31),  and  would 


FIG  30.— STRATIF 


RING. 


120 


XEBULAR   LIFE. 


FIG.  31.— NEBULOUS   RING   UNDE 

RUPTUKE. 


finally  part.   The  annular 
mass  would  now  rapidly 
gather  itself  into  a  sphe- 
roid (Figure  32),  which 
would    continue    revolv- 
ing in  a  path  determined 
by  the    position   of   the 
transformed     ring.        It 
seems  possible  that  such 
process    of    aggregation 
might  take  place  at  two 
or  more  points  in  a  ring, 
and  this  is  the  view  which 
was  entertained   by  La- 
place.    In  such  case,  there  would  result  a  corresponding 
number  of  spheroids;  but  these  would  sooner  or  later  co- 
alesce in  one.     No  two  bodies 
could    continue    permanently 
to  revolve  in  one  orbit. 

C.  S.  Cornelius,  in  an  essay 
of  much  originality,  has  ad- 
vanced the  opinion  that  the 
separated  ring  would  attract 
to  itself  some  neighboring  por- 
tions of  the  abandoned  nebu- 
lous spheroid.  These  portions, 
he  assumes,  would  join  the 
ring  with  a  smaller  rotational 

momentum,  and  the  union  of  parts  thus  differing  in  energy 
of  rotation  would  strain  the  ring  to  such  an  extent  as  to 
rupture  its  continuity.  Each  of  the  resulting  partial  sphe- 
roids would  rotate  in  the  original  direction.  But  the  larger 
of  these  would  eventually  unite  all  the  others  in  itself.* 

*  Vereinigte  nun  dcr  sich  ablOsende  Ring  durch  Auziehung  die  zuniichst 
angrenzenden  Theile  der  Dunstkugel  mit  seiner  Masse,  so  musste  derselbe  ver- 


FIG.  32.— SPHERATION  OP  A  NEBU- 
LOUS RING. 


SPHERATION   OF  RIKGS.  121 

The  breaking  up  of  a  set  of  concentric  rings  would  re- 
sult in  a  corresponding  number  of  rotating  bodies,  which 
would  be  likely,  in  some  cases,  to  remain  isolated. 

By  some  such  means  repeated  a  number  of  times,  the 
entire  nebula  would  be  reduced  to  an  assemblage  of  par- 
tial nebulous  masses,  all  revolving  in  orbits  about  the 
original  centre  of  gravity.* 

2.  Rotation  of  Resulting  Mass. — It  may  be  set  down 
as  a  necessary  result  that  the  mass  derived  from  a  ring 
would  possess  a  rotary  motion  about  some  axis.  By  an 
infinity  of  chances  to  one,  the  resultant  of  all  the  external 
forces  acting  upon  it  would  not  pass  through  the  centre  of 
gravity.  But  the  mode  of  connection  between  the  derived 
spheroid  and  the  parent  mass  would  be  the  principal  de- 
terminative circumstance.  The  lines  of  interaction  be- 
tween the  two  would  be  located  nearly  in  the  plane  of  the 
equator  of  the  original  mass;  and  hence  the  probable 
rotation  would  be  in  that  plane.  We  have  then  to  con- 
sider whether  the  rotation  would  be  direct — that  is,  in  the 
same  direction  as  that  of  the  primitive  nebula — or  retro- 
grade. 

The  ring  before  spheration  possessed  a  certain  amount 
of  breadth.  Laplace  conceived  that  the  external  and  in- 
ternal zones  of  the  ring  would  rotate  with  the  same  angu- 
lar velocity,  which  would  be  the  case  with  a  solid  ring; 
but  the  principle  of  equal  areas  requires  the  inner  zones  to 
rotate  more  rapidly  than  the  outer.  The  determination  of 
the  relative  velocities  of  the  outer  and  inner  zones  is  the 

moge  der  abweichenden  Rotationsgeschwindigkeit  und  Schwungkraft  der  ange- 
zogenen  Theiln,  so  wie  auch  in  Folge  von  Molecularkraften  seinen  Zusammen- 
hang  verlieren  und  in  mehrere  Stucke  zerfallen.  *  *  *  Das  grGsste  Bruch- 
etiick  des  Ringes  mochte  nun  insgemein  die  kleineren  Stucke  herbeiziehen  und 
sie  mit  seiner  Masse  vereinigen.  (Entstehung  der  Welt,  p.  18.  Leipzig,  1870). 

*  The  stability  of  a  ring,  while  possible,  is  something  with  a  high  order  of 
chances  against  it.  See  Maxwell:  On  the  Stability  of  the  Motion  of  Saturn's 
rings,ai\A  B.  Peirce,  Gould's  Astronomical  Journal,  ii,  17, 18. 


122  NEBULAR   LIFE. 

solution  of  the  problem  of  the  direction  of  the  rotation  of 
the  derived  spheroid. 

I  have  maintained,  when  speaking  of  the  periodicity  of 
ring-formation,  that  friction,  cohesion,  and  mutual  attrac- 
tions of  the  parts  of  a  separating  ring  must  exist  to  such 
an  extent  as  to  render  annulation  periodic.  If  I  am  cor- 
rect in  this  opinion,' it  is  manifest  that  friction,  cohesion, 
and  mutual  attractions  of  the  outer  and  inner  zones  of  the 
ring  would  tend  to  equalize  the  angular  velocities  of  the 
outer  and  inner  portions.  Let  us  assume,  in  the  first  place, 
that  the  equalization  of  external  and  internal  motions 
becomes  nearly  complete.  The  remotest  side  of  the  derived 
spheroid  would  then  accomplish  a  revolution  about  the 
parent  mass  in  the  same  time  as  the  nearer  side.  The 
nearer  side  would  remain  turned  toward  the  parent  mass 
during  the  entire  revolution.  This  is  equivalent  to  saying 
the  derived  mass  would  complete  one  rotation  on  its  axis 
while  performing  one  revolution  in  its  orbit.  The  motion 
would  be  direct.  The  relations  assumed  are  the  condition 
of  direct  rotary  motion. 

If  we  had  no  concomitant  interference  to  consider,  it 
is  manifest  that  the  direct  rotation  thus  inaugurated  would 
be  accelerated  by  subsequent  cooling  and  contraction,  and 
the  primitive  synchronism  of  axial  and  orbital  motions 
would  immediately  cease  to  exist.  As  the  final  amount  of 
acceleration  in  a  rotating  spheroid  contracting  in  conse- 
quence of  loss  of  heat,  depends  on  the  amount  of  contrac- 
tion, and  this  depends  on  the  amount  of  matter,  it  is 
obvious  that  the  final  velocity  of  rotation  must  be  propor- 
tional to  the  mass.  Large  masses  in  advanced  stages  of 
their  existence  should  have  a  more  rapid  rotation  than 
small  masses  in  corresponding  stages.  All  masses  must 
experience  acceleration  proportioned  to  the  total  amount 
of  contraction  undergone. 

The  derived  mass  might  be  of  such  magnitude  as  to 


SPHERATION    OF    RINGS.  123 

retain  its  nebulous  state  long  enough,  and  acquire  rotary 
acceleration  enough,  to  enter,  on  its  own  part,  upon  a 
process  of  annulation.  This  system  of  disintegration,  so 
far  as  concerns  the  forces  which  inaugurated  it,  must  con- 
tinue until  the  augmentation  of  paracentric  force  can  no 
more  become  sufficient  to  equalize  the  sum  of  the  force  of 
gravitation  and  the  resistance  of  rigidity.  The  whole  his- 
tory of  acceleration  and  disintegration  is  independent  of 
the  direction  of  the  motion. 

The  subsequent  evolutions  thus  enunciated  would  begin 
immediately  on  the  spheration  of  a  ring,  if  no  external 
interference  were  experienced.  To  this  point  I  shall  here- 
after return. 

Let  us  next  consider  what  would  happen  if  the  relative 
velocities  of  the  outer  and  inner  zones  of  the  nebulous 
ring  should  be  determined  in  full  accordance  with  the 
principle  of  equal  areas.  In  this  case,  the  velocity  of  the 
inner  zone  would  as  many  times  exceed  that  of  the  outer, 
as  the  square  of  its  distance  from  the  centre  of  motion  is 
less  than  the  square  of  the  distance  of  the  outer  zone  from 
the  centre  of  motion.  So  far  as  this  circumstance  is  con- 
cerned, the  nearer  side  of  the  derived  spheroid  would  tend 
to  perform  its  circuit  about  the  primitive  centre  in  less 
time  than  the  remoter  side.  But,  as  we  assume  all  parts 
to  be  held  together,  the  result  would  be  a  retrograde  rota- 
tion of  the  derived  spheroid.  The  subsequent  cooling, 
contraction  and  acceleration  would  proceed  exactly  as  in 
the  case  of  direct  motion. 

Now,  reflection  upon  this  subject  has  led  me  to  the 
conviction  that  the  physical  relations  accompanying  the 
spheration  of  a  ring  are  not  such  as  to  determine  uniformly 
either  direct  or  retrograde  motion.  Under  certain  circum- 
stances the  motion  would  be  direct;  under  other  circum- 
stances, it  would  be  retrograde.  It  seems  probable  the 
consistency  of  a  nebulous  mass  and  its  rate  of  condensa- 


124:  NEBULAR   LIFE. 

tion  internally  would  be  such  generally,  that  the  actual 
relation  of  velocities  of  the  outer  and  inner  zones  would 
be  somewhere  between  uniformity  and  that  determined  by 
the  principle  of  equal  areas. 

Since  we  may  fairly  assume  the  influence  of  friction, 
cohesion  and  mutual  gravitation  of  parts  to  have  some 
real  existence  in  a  nebulous  ring,  there  must  be  consti- 
tuted, so  far,  a  tendency  to  equal  angular  velocities  in  the 
inner  and  outer  zones,  and  a  corresponding  predisposition 
to  direct  motion.  So  far  as  the  law  of  equal  areas  is  con- 
cerned, there  must  exist  a  predisposition  to  retrograde 
motion.  These  two  predispositions  must  always  exist, 
and  they  must  always  contend  against  each  other.  The 
preponderance  of  the  one  will  give  direct  motion;  the 
preponderance  of  the  other  will  give  retrograde  motion. 

But  we  understand  the  principle  of  equal  areas  is  an 
absolute  physical  law  whose  action,  disregarding  mass 
(since  in  this  question  we  may  deal  always  with  equal 
masses),  is  always  with  efficiency  inversely  proportional  to 
the  square  of  the  radius  vector.  The  measure  of  this 
efficiency  is  the  difference  of  the  squares  of  the  radii 
vectores  of  the  outer  and  inner  zones  of  the  ring.  Against 
this  contends  a  set  of  influences  which  vary  with  circum- 
stances. Friction  will  vary  with  the  pressure  upon  the 
contiguous  parts,  and  this  will  vary  with  the  mass  in  a 
section  of  the  ring.  Cohesion  will  vary  with  the  kind  and 
state  of  the  matter.  The  mutual  attraction  of  parts  will 
vary  with  the  mass  in  the  section  and  the  distances  of  the 
centres  of  the  partial  masses. 

Under  what  circumstances  will  these  variable  influences 
attain  a  maximum  ?  In  other  words,  when  will  direct 
motion  be  most  likely  to  ensue?  Manifestly,  when  the 
nebulous  matter  is  most  condensed,  and  most  acted  upon 
by  the  attraction  of  the  parent  mass.  That  is,  when  the 


SPHERATIOX    OF   RINGS.  125 

progress  of  annulation  has  reached  somewhat  toward  the 
central  portion  of  the  nebula.  When  will  the  opposing 
principle  of  equal  areas  possess  least  efficiency?  Mani- 
festly, when  the  rings  are  narrowest.  That  is,  when  the 
density  of  the  nebula  reduces  the  period  during  which  a 
forming  ring  may  continue  to  receive  accessions.  In  other 
words,  in  the  later  stages  of  annulation.  It  is,  therefore, 
in  the  later  stages  of  annulating  life  that  the  predisposi- 
tion to  direct  motion  is  greatest,  and  the  predisposition  to 
retrograde  motion  is  least.  It  is  perfectly  rational  to  sup- 
pose, finally,  that  the  derived  spheroids  resulting  from 
later  evolutions  should  possess  direct  motion. 

These  conditions  are  all  reversed  in  the  earlier  stages 
of  the  annulating  history  of  a  nebula.  In  the  peripheral 
portion  of  the  nebula,  diminished  gravitation  operates  less 
efficiently  in  restraining  the  accession  of  matter  to  the 
forming  ring,  and  thus  allows  the  ring  to  attain  greater 
.breadth.  In  the  primitive  epoch  also,  the  great  tenuity  of 
the  matter  implies  diminished  friction  and  cohesion,  and 
correspondingly  implies  a  more  rapid  contraction,  and  a 
greater  prolongation  of  the  period  of  ring-growth.  It 
implies,  in  other  words,  a  greater  breadth  of  ring,  and  a 
greater  efficiency  of  the  principle  of  equal  areas;  and  a 
correspondingly  stronger  predisposition  toward  retrograde 
motion.  It  is  perfectly  rational  to  suppose,  finally,  that 
the  derived  spheroids  resulting  from  earlier  evolutions 
should  possess  retrograde  motion. 

This  conception  of  physical  relations  renders  it  proba- 
ble that  the  same  nebula  would  evolve  earlier  secondaries 
inheriting  retrograde  axial  motions,  and  later  secondaries 
inheriting  direct  axial  motions.  This  state  of  things 
partially  exists  in  our  solar  system.  But  the  considerable 
deviation  of  the  equators  of  the  Neptunian  and  Uranian 
systems  from  coincidence  with  the  plane  of  the  sun's  equa- 


126  NEBULAR   LIFE. 

tor   should  cause  hesitation  in  accepting   the   foregoing 
views  as  a  full  explanation  of  their  anomalous  motions.* 

*The  reasoning  here  employed  may  be  made  a  little  more  tangible  by  the 
use  of  algebraic  notation. 

Let  R'  =  radius  of  inner  stratum  of  ring. 
R"=  radius  of  outer  stratum  of  ring. 
•v'  =  linear  velocity  of  inner  stratum  of  ring. 
v"—  linear  velocity  of  outer  stratum  of  ring. 
Then,  supposing  the  angular  velocities  of  the  two  strata  equal,  we  have 


This  is  the  condition  of  direct  motion. 

But  supposing  the  outer  and  inner  strata  to  have  velocities  according  to  the 
law  of  equal  areas,  we  have 

R'" 

V  :  V"::  R"1  :  R" ;  .'.  v'=v"  ~. 

This  is  the  condition  of  retrograde  motion. 

When  the  value  of  v'  is  at  a  certain  point  between  v"  ^  and  v"  -sr^^  there 

will  be  no  rotation.    Let  x  represent,  the  excess  of  that  value  over  v"  j^,  and 

R"a 
y,  the  excess  of  v"  ^-5  over  the  same  value.    Then 


This  is  the  condition  of  no  rotation. 

But  any  change  in  values  which  will  make 


will  result  in  direct  motion.    This  inequation  will  arise 

(a)  When  R'  increases  or  R"  diminishes  —  that  is,  when  the  breadth  of  the 
ring  diminishes. 

(b)  When  R'  and  R"  diminish  equally  in  arithmetical  ratio  —  that  is,  when 
they  pertain  to  a  smaller  ring  having  the  same  breadth  and  rotary  velocity. 

(c)  When  v"  diminishes,  the  other  quantities  remaining  constant,  or  R'  and 
R"  also  diminishing  in  equal  arithmetical  ratio—  a  condition  in  the  later  annula- 
tion  of  a  mass  having  great  central  condensation. 

Also,  any  change  in  values  which  will  make 


will  result  in  retrograde  motion.    This  inequation  will  arise 

(a)  When  R'  diminishes  or  R"  increases—  that  is,  when  (he  breadth  of  the 
ring  increases. 

(b)  When  R'  and  R"  increase  equally  in  arithmetical  ratio—  that  is,  when 
they  pertain  to  a  larger  ring  having  the  same  breadth  and  rotary  velocity. 

(c)  When  v"  increases,  the  other  quantities  remaining  constant,  or  R'  and 
R"  also  increasing  in  equal  arithmetical  ratio—  a  condition  in  the  earlier  annula- 
tions  of  a  mass  having  great  central  condensation. 

From  all  which  it  appears  that  while  direct  motions  must  probably  prevail 


SPHERATIOST    OF    RINGS.  127 

It  ought  to  be  remarked  also,  that  the  probability  of 
retrograde  motions  in  the  earlier  history  of  annulation 
would  increase  with  the  volume  of  the  nebula.  Because, 
in  a  larger  nebula,  the  difference  between  peripheral  and 
central  condensation  is  greater,  and  here  would  exist  a 
greater  difference  in  the  influences  of  friction  and  cohesion 
in  the  earlier  and  later  processes  of  annulation.  We 
should  infer,  therefore,  that  in  a  relatively  small  nebula 
all  the  rotations  would  be  direct.  This  inference  is  exem- 
plified in  the  Saturnian  and  Jovian  systems  of  satellites; 
and  probably  also  in  the  Uranian  and  Neptunian,  where 
direct  motion  would  be  motion  in  the  direction  of  the 
rotation  of  the  primaries. 

Some  investigators  of  this  subject  have  assumed  the 
position  that  the  primitive  rotation  of  the  derived  mass 
must  in  all  cases  be  retrograde.*  They  ignore,  however, 
the  influence  of  friction  and  cohesion.  Others  have  at- 
tempted to  show  that  retrograde  motions  either  must  or 
might  arise  in  the  earlier  annulation-history,  while  direct 
motion  would  ensue  in  the  later  history,  f  The  conclusion 
is  the  same  which  I  have  reached  by  a  method  which  seems 
more  intelligible  and  convincing.  Professor  Hinrichs 
shows  that  the  rotary  motion  will  be  direct,  zero  or  retro- 
grade, according  as  the  primitive  density  of  the  nebula  in 
the  part  where  the  orbit  becomes  located,  was  greater, 
equal  to  or  less  than  a  certain  quantity  depending  on  the 
position  of  the  orbit  in  the  ring,  and  on  the  law  of  varia- 
tion of  the  density.  If  the  variation  in  density  were  zero, 

in  the  regions  nearer  the  centre,  retrograde  motions  may  arise  in  the  regions 
remoter  from  the  centre. 

It  may  be  added  that  the  actual  occurrence  of  direct  motions  in  our  system 
is  evidence  that  the  inner  and  outer  strata  of  the  corresponding  rings  did  not 
possess  velocities  adjusted  fully  to  the  law  of  equal  areas. 

*  D.  Kirkwood,  Amer.  Jour.  Sci.,  II,  xxxviii,  2-4;  D.  Trowbridge,  Amer.  Jour. 
Sci.,  II,  xxxix,  25-6. 

t  G.  Hinrichs,  Amer.  Jour.  Sci.,  II,  xxxvii,  51 ;  M.  Faye,  Comptes  Rendus,  xc, 
640. 


128  NEBULAR   LIFE. 

all  the  derived  spheroids  would  have  direct  motion.  But  if 
the  density  diminished  from  the  centre,  however  slowly, 
then  the  earlier  formed  secondaries  would  have  retrograde 
motion,  and  the  later  direct  motion.  The  conclusion  is 
based  solely  on  relations  of  density,  interannular  spaces, 
and  position  of  resulting1  orbit  in  the  ring. 

Mr.  Faye,  adopting  an  analytical  expression*  for  the 
law  of  increase  of  density  toward  the  centre,  determines 
that  the  linear  velocities  of  the  internal  parts  will  go  on 
increasing  in  diminishing  ratio  from  the  circumference  to 
a  certain  distance  from  the  centre,  when  the  linear  rotary 
velocities  will  begin  to  decrease.  Thus  he  concludes  that 
the  annulating-life  of  a  nebula  would  be  divided  into  two 
periods,  during  the  first  of  which  the  rotary  motions  of 
the  derived  masses  would  be  retrograde,  while  during  the 
other  they  would  be  direct.  But  it  does  not  appear  evi- 
dent that  the  superior  linear  velocity  of  the  remoter  parts 
would  suffice  as  a  sole  cause  for  effectuating  retrograde 
motions.  Such  motion  must  result  from  a  certain  ratio  of 
outer  and  inner  velocities,  and  this  depends,  as  I  have 
shown,  on  the  breadth  of  the  ring  and  the  influence  of 
friction  and  cohesion.  M.  Faye  takes  no  account  of  the 
influence  of  friction  and  cohesion,  while,  so  far  as  I  under- 
stand the  subject,  the  possibility  of  direct  motion  at  any 
stage  depends  on  the  preponderating  influence  of  friction 
and  cohesion. 

It  is  not  necessary  to  assume  that  axial  rotation  would 
be  impressed  only  by  the  forces  already  mentioned.  If 
two  or  more  spheroidal  masses  should  result  from  the 
rupture  of  a  nebulous  ring,  and  should  afterward  coalesce, 
their  impact  must  generate  a  rotation,  as  heretofore  ex- 
plained. But  such  rotation  would  as  probably  be  in  one 

*DI1—  0I/ if~)'  wnerc  D  is  tne  central  density  of  the  nebula,  R  the  ra- 
dius of  its  equator,  r  the  distance  from  any  point  to  the  center,  n  an  arbitrary 
positive  number,  and  ft  a  very  small  fraction. 


SPHERATION   OF   KINGS.  129 

direction  as  another,  except  so  far  as  the  synchronous 
rotation,  always  necessarily  existing  in  the  primitive  stage, 
should  predispose  to  a  rotation  in  the  established  direc- 
tion.* In  spite  of  this  there  ought  to  be  some  cases  in 
which  the  motion  would  be  retrograde,  or  the  axis  of 
rotation  far  from  perpendicular  to  the  plane  of  the  orbit. 
In  addition  to  this,  it  remains  to  be  said  that  every  exter- 
nal attraction  experienced  by  the  forming  spheroid,  until 
its  form  should  have  attained  mathematical  symmetry, 
would  tend  to  inaugurate  rotation,  or  change  any  existing 
rotation,  under  any  of  the  conditions  pointed  out  in  dis- 
cussing the  origin  of  nebular  rotation  in  general. 

3.  The  Influence  of  Cosmic  Tides  upon  the  Rotation  of 
the  Derived  Spheroid.\ — We  come  now  to  consider  the 
interferences  before  alluded  to.  Supposing  the  derived 
spheroid  to  be  affected  by  a  motion  of  rotation,  the  ac- 
celeration of  its  rotation  would  not  immediately  proceed 
step  by  step  with  the  progress  of  cooling  and  contraction. 
Such  acceleration  would  be  opposed  by  the  prolate  de- 
formation which  would  arise  through  the  differential  mo- 
menta of  its  own  parts,  and  the  differential  attractions  of 
the  central  residual  mass  exerted  on  a  mass  of  such 
mobility  of  parts  as  the  incandescent  vapor  which  we  are 
considering.  By  hypothesis,  the  centre  of  gravity  of  this 
new  sphere  is  at  such  distance  from  the  parent  mass  as  to 
be  poised  between  centripetal  and  centrifugal  tendencies. 
The  remoter  point  a,  Fig.  33,  must  therefore  experience 
an  excess  of  centrifugal  tendency  in  consequence  of  its 
greater  velocity,  and  would  only  be  retained  by  the  attrac- 
tion of  the  derived  mass.  It  would  indeed  tend  to  retire 
from  c  until  the  centrifugal  force  due  to  rotation  about  o 

*  In  this  connection  the  various  inclinations  of  the  planetary  axes  in  the 
solar  system  are  somewhat  suggestive.  The  inclination  of  Venus  amounts  to 
50°,  while  that  of  Uranus  and  Neptune  is  generally  considered  to  be  over  90°. 

t  The  influence  of  tides  in  cosmical  history  will  be  more  fully  considered 
hereafter  in  connection  with  planetary  vicissitudes. 
9 


130 


NEBULAR   LIFE. 


FIG.  33.— PROLATENESS  AND  ROTATION 
OF  THE  DERIVED  SPHERIOD. 


should  be  balanced  by 
the  central  attraction 
directed  toward  c.  On 
the  contrary,  the  parts 
at  b,  having  now  the 
same  angular  velocity 
as  the  other  parts,  but 
a  slower  actual  veloci- 
ty, the  centripetal  ten- 
dency would  be  in 
excess,  and  they  would 
extend  toward  o,  until 
this  excess  should  be 
counterbalanced  by 
gravitation  toward  c.* 
Concurrent  with  these  actions  would  be  the  difference  of 
attractions  exerted  by  the  parent  mass  upon  a  and  b, 
raising  veritable  tides  in  those  opposite  regions.  Thus,  a 
prolate  spheroid  would  come  into  existence,  whose  stabil- 
ity would  persist  for  a  certain  period.  But  the  contrac- 
tion of  the  mass  and  the  increasing  effort  to  accelerate 
the  gyration  might  ultimately  destroy  the  synchronism 
between  axial  and  orbital  motions. 

There  is  this  further  to  be  said  of  a  prolate  aeriform 
mass  situated  as  described,  and  constrained  toward  accel- 
erated rotation.  It  must  not  be  viewed  as  a  rigid  body. 
All  its  parts  possess  excessive  mobility.  The  superficial 
particles  at  «,  under  an  impulse  to  accelerated  motion, 
would  flow,  on  the  assumption  of  an  effort  toward  direct 
motion,  in  the  direction  of  the  arrow,  toward  by  if  the 
general  mass  were  restrained  from  a  consentaneous  move- 
ment. Parts  at  b  would  experience  a  similar  tendency 

*  While  this  reasoning  discloses  a  true  cause  of  prolateness  or  tidal  eleva- 
tion, it  is  not  conceived  to  be  the  most  efficient  cause  of  tides,  especially  upon 
the  larger  of  two  spheroids  tidally  connected  together  and  differing  greatly  in 
mags. 


SPHERATION   OF   RINGS.  131 

to  flow  in  the  same  direction.  Thus  superficial  currents 
would  be  established;  and  these  would  deepen  and  involve 
more  and  more  of  the  whole  mass.  In  proportion  as  the 
flow  of  these  currents  should  be  established  and  deepened, 
the  attainment  of  accelerated  rotation  of  the  general 
mass  would  be  accomplished;  and  ultimately  the  whole 
mass  would  possess  a  rotation  more  rapid  than  the  orbital 
rotation.  Thus,  perhaps,  might  an  axial  rotation  be  ac- 
quired nearly  corresponding  with  the  acceleration  due  to 
the  contraction  of  the  mass  after  the  earliest  epoch  of 
spheration.  But  the  prolateness  would  never  disappear, 
and  would  only  diminish  in  proportion  as  the  molecular 
mobility  should  diminish  by  condensation,  by  cooling  or 
some  other  cause.  Different  sides  of  the  derived  spheroid 
would  consequently  be  raised  successively  into  a  tidal  pro- 
tuberance. The  consequence  of  this  would  be  a  perpetual 
relative  displacement  of  the  different  parts  in  respect  to 
each  other,*  which  might  be  compared  with  the  effect  of 
rolling  an  india  rubber  ball  between  the  hand  and  a  surface 
on  which  the  ball  is  pressed. 

The  prolate  condition  of  the  new  spheroid  may  be  con- 
templated without  regard  to  the  relative  motions  of  its 
constituent  parts.  It  hangs  balanced  by  a  support  fixed 
at  the  centre  of  the  forces  acting  upon  it.  It  is  manifest, 
therefore,  that  any  new  force  applied  to  it,  having  a  com- 
ponent making  an  oblique  angle  with  c  O  (Figure  33), 
must,  unless  such  component  pass  through  the  centre  of 
inertia,  disturb  the  equilibrium  of  the  position  of  the  body. 
In  other  words,  the  prolate  axis,  a  b,  would  be  inclined  so 
as  to  make  an  angle  with  c  O.  The  actual  direction  of 
the  motion  would  be  a  resultant  of  this  perturbative 
action  and  the  existing  strain  toward  accelerated  rotation. 
It  is  supposable  that  this  strain  might  be  so  nearly  equal 

*  I  shall  employ  this  principle  in  explaining  the  origin  and  phenomena  of 
vulcanicity  in  the  earth. 


132  NEBULAR   LIFE. 

to  the  synchronous  tendency  that  the  power  overcoming 
this  tendency  would  only  need  to  be  comparatively  slight, 
and  that,  consequently,  the  actual  movement  of  the  mass 
would  be  about  an  axis  very  nearly  normal  to  the  plane  of 
its  orbit,  and,  on  the  assumption  made,  in  the  direction  of 
the  orbital  motion.  I  see  no  ground  for  assuming  that 
such  a  relation  of  perturbative  and  synchronizing  forces  is 
unlikely  to  arise  in  a  nebulous  spheroid  resulting  from  the 
spheration  of  a  nebulous  ring. 

Should  the  disturbing  action  be  temporary,  the  body 
would  swing  back  to  the  position  determined  by  the  origi- 
nal forces;  or  rather,  it  would  swing  past  that  position 
and  begin  an  oscillatory  movement  which  would  be  per- 
petuated until  interfered  with  by  some  other  external  dis- 
turbance. It  is  manifest  that  this  oscillation  of  the  line 
ab  might  be  in  any  plane.  If  not  exactly  in  the  plane  of 
the  orbit,  or  in  a  plane  at  right  angles  with  this,  the 
motion  might  be  resolved  into  two  components,  one  lying 
in  each  of  these  planes.  Thus  would  arise  movements 
analogous  to  those  ¥  known  in  astronomy  as  nutations  and 
librations.  It  must  not  be  supposed,  however,  that  the 
longer  axis  of  the  figure  would  receive  the  whole  of  this 
motion,  since  attraction  toward  O,  together  with  inter- 
molecular  freedom  of  motion,  would  cause  this  axis  to  lag 
behind  during  every  oscillation  of  the  former  axis  away 
from  the  line  c  O.  In  other  words,  just  so  far  as  intermo- 
bility  of  parts  exists,  the  prolate  axis  would  be  maintained 
in  the  direction  cO;  and  it  would  be  swung  out  of  this 
direction  only  in  proportion  as  the  mass  might  have  pro- 
gressed toward  a  state  of  rigidity. 

According  to  the  conception  here  set  forth  respecting 
the  formation  of  a  prolate  spheroid,  the  synchronism  of 
orbital  and  axial  movements  might  be  destroyed  only  after 
cooling  and  contraction  should  have  developed  sufficient 
tendency  to  accelerated  motion  to  overcome,  in  conjunc- 


SPHEKATI01S"   OF    RINGS.  133 

tion  with  any  perturbative  action,  the  actions  holding  the 
line  a  b  in  its  position.  If,  while  this  acceleration  is  be- 
coming developed,  the  mass  should  attain  approximate 
rigidity,  the  superficial  currents  before  mentioned  would 
be  arrested,  and  would  cease  to  contribute  their  agency 
toward  an  increased  rotation  of  the  general  mass;  but, 
on  the  contrary,  the  crushing  process  of  maintaining  pro- 
lateness  would  be  greatly  opposed,  and  the  prolateness 
would  be  correspondingly  diminished,  together  with  its 
resistance  to  heterochronous  rotation. 

The  conservation  of  synchronous  motions  would  be 
promoted  by  an  action  not  yet  mentioned.  Conceiving 
each  tidal  protuberance  to  be  represented  by  a  point  at 
the  apex,  it  appears  that  the  one  on  the  nearer  side  by 
being  brought  under  an  increased  centripetal  force  will 
suffer  a  tendency  to  accelerated  motion  in  its  orbit.  The 
effect  of  this  would  be  to  set  up  a  retrograde  rotary  motion 
in  the  derived  spheroid.  On  the  contrary,  the  point  at 
the  apex  of  the  anti-tide,  by  being  brought  under  a  dimin- 
ished centripetal  force,  will  suffer  a  tendency  to  retarded 
motion  in  its  orbit.  The  effect  of  this  will  also  be  to  set 
up  a  retrograde  rotary  motion  in  the  derived  spheroid. 
This  factor  unites  with  intermolecular  friction,  cohesion 
and  inertia  in  delaying  the  establishment  of  heterochron- 
ous motions. 

A  rigid  body,  or  any  solid  body  approximately  rigid 
and  incompressible,  possessing  such  prolateness  as  to 
result  in  synchronism  of  axial  and  orbital  motions,  could 
never  have  this  synchronism  destroyed  except  by  a  disturb- 
ance exerted  from  without.  This,  therefore,  is  a  relation 
of  orbital  and  axial  motions  which  ought  to  result  some- 
times in  the  progress  of  the  history  whose  earlier  chapters 
we  are  endeavoring  to  trace.  It  would  be  more  likely  to 
result  in  proportion  as  the  process  of  refrigeration  should 


134  NEBULAR    LIFE. 

be  relatively  more  rapid.     This  would  take  place  in  nebu- 
lous masses  relatively  smaller. 

4.  Ultimate  Synchronism  of  Axial  and  Orbital  Mo- 
tions.— It  should  be  mentioned  in   this  connection,  that 
synchronous   movements  having  been   once  overcome,  in 
the  early  stage,  there  would  be  felt  a  tendency  to  their 
reproduction,  under  certain  conditions,  during  a  later  stage 
of   development.     While    the   nebulous   condition    exists, 
contraction  would  be  rapid  and  great  in  amount.       The 
resistance  offered  by  prolateness  to  the  destruction  of  syn- 
chronism, would  perhaps,  therefore,  in  all  cases,  be  com- 
pletely overcome,  and  a  rapid  rotary  motion  would  be  a 
nearly  uniform  incident  in  the  history  of  cooling.     But, 
as    the    tidal    protuberance,  even   if   solidification    should 
ensue,  can  never  cease  to  exist,  its  influence  in  opposing 
rapid  rotation  will  never  be  removed.     When,  therefore, 
the  rate  of  contraction  and  consequent  tendency  to  accel- 
erated rotation  has  been  much  reduced  by  an  advanced 
stage  of  cooling,  or  by  incrustation  or  solidification,  the 
resistance  of  the  tidal  prolateness,  which  does  not  diminish 
accordingly,  must  again  tend  to  equilibrate  and  neutralize 
the  rotating  tendency.    This  effect,  upon  a  globe  perfectly 
solidified,  would  probably  reach  a  maximum  in  those  cases 
where  fluids  like  oceans  should  rest  in  basins  with  solid 
barriers  against  which  the  fluid  tide  could  act.     Thus  the 
condition  of  synchronous  axial  and  orbital  revolutions  is 
also  an  incident  in  the  advanced  stages  of  the  cooling- 
history. 

5.  Summary. — We    have    thus   been   occupied   with 
the  difficult  question  of  the  direction  and  velocity  of  the 
rotation  which  would   arise  in  a  spheroid  resulting  from 
the  spheration  of  a  nebulous  ring  detached  from  a  central 
rotating  mass.       The   conclusions   reached   may   be  sum- 
marized as  follows : 

(1.)  Rotation  would  arise  with  the  process  of  sphera- 


SPHERATION"   OF   RINGS.  135 

tion,  and  its  axis  would  most  probably  be  at  right  angles 
with  the  plane  of  the  nebular  equator. 

(2.)  The  direction  of  the  rotation  would  be  determined 
by  the  relation  of  the  velocities  of  the  outer  and  inner 
zones  of  the  ring. 

(3.)  If  all  parts  of  the  ring  rotated  with  nearly  the 
same  angular  velocity,  the  resulting  rotation  in  the 
spheroid  would  be  direct. 

(4.)  If  the  inner  zone  rotated  with  increased  velocity,  in 
accordance  with  the  law  of  equal  areas,  the  rotation  would 
be  retrograde. 

(5.)  Friction  and  cohesion  and  mutual  attraction  of  parts 
would  have  a  tendency  to  equalize  angular  velocities,  and 
thus  to  create  a  strain  toward  direct  motion. 

(6.)  If  this  strain  were  unequal  to  the  tendency  toward 
motion  under  the  law  of  equal  areas,  the  rotation  would 
be  retrograde;  if  it  equalled  that  tendency  there  would 
be  no  rotation;  if  it  exceeded  it,  the  rotation  would  be 
direct. 

(7.)  The  strain  toward  direct  motion  would  be  least 
when  the  nebulous  matter  is  tenuous,  for  then  friction  and 
cohesion  would  be  least,  and  the  influence  of  gravitation 
would  be  least  felt.  The  strain  toward  retrograde  motion 
would  be  greatest  when  the  ring  is  widest,  for  then  the 
acceleration  of  the  inner  zone  is  greatest.  The  conditions 
of  least  strain  toward  direct  motion  and  greatest  toward 
retrograde  motion  would  concur  in  the  earlier  annulating 
stage  of  the  nebula. 

(8.)  The  strain  toward  direct  motion  would  be  greatest 
when  the  nebulous  matter  is  most  dense,  for  then  friction 
and  cohesion  would  be  greatest,  and  the  influence  of 
gravitation  would  be  most  felt.  The  strain  toward  retro- 
grade motion  would  be  least  when  the  ring  is  narrowest, 
for  then  the  acceleration  of  the  inner  zone  would  be  least. 
The  conditions  of  greatest  strain  toward  direct  motion 


136  NEBULAR   LIFE. 

and  least  toward  retrograde  motion  concur  in  the  later 
annulating  stage  of  the  nebula. 

(9.)  The  rotation,  if  direct,  would  at  first  probably  be 
synchronous  with  the  orbital  revolution,  and  the  derived 
spheroid  would  be  prolate.  This  prolateness  would  tend 
to  persist,  (a)  In  consequence  of  the  imperfect  intermo- 
bility  of  parts  in  the  spheroid.  (#)  In  consequence  of  an 
adjustment  of  parts  having  different  densities,  so  that  the 
most  and  least  dense  would  be  ranged  about  the  poles  of 
the  prolate  axis. 

(10.)  The  progressive  contraction  of  the  derived  spheroid 
would  result  in  a  perpetual  tendency  to  rotate  more 
rapidly;  and  this  tendency  might  overcome  the  tendency 
to  synchronous  movements.  This  would  be  the  more 
likely  as  the  latter  tendency  would  diminish  with  the 
increase  of  the  square  of  the  interval  between  the  centres 
of  gravity  of  the  derived  and  original  masses. 

Memorandum. — This  interval  would  increase,  (a)  By 
the  progressive  shrinkage  of  the  central  mass,  (b)  As  a 
consequence  of  the  diminished  centripetal  force,  (c)  As 
the  result  of  any  eccentric  motion  which  may,  in  some 
cases,  have  been  imparted  to  the  derived  mass  at  the  epoch 
of  its  separation  from  the  primitive  mass. 

(11.)  In  a  derived  spheroid  possessing  great,  but  un- 
equal, intermolecular  mobility,  the  establishment  of  super- 
ficial currents,  gradually  deepening  and  involving  the  whole 
mass,  would  tend  to  destroy  primitive  synchronous  move- 
ments. 

Memorandum. — The  prolateness  of  the  derived  mass 
would,  however,  be  maintained,  and  would  diminish  only 
in  proportion  as  its  rigidity  should  increase. 

(12.)  Perturbative  action  having  a  component  making 
an  oblique  angle  with  the  prolate  axis  might  overcome  any 
preponderating  tendency  to  synchronous  motions. 

(13.)  In  a  rigid  prolate  body  synchronously  rotating, 


SPHERATION    OF    RINGS.  137 

only  external  perturbative  action  couid  ever  destroy  the 
synchronism. 

(14.)  Rotation  would  also  be  caused  by  the  inevitable 
ultimate  coalescence  of  the  two  or  more  masses  into  which 
it  is  supposable  that  an  unstratified  nebulous  ring  might, 
in  some  instances,  be  separated.  The  discordant  positions 
of  the  rotational  axes  resulting  from  this  cause  are,  how- 
ever, not  distinctly  apparent  among  the  phenomena  of  the 
solar  system. 

(15.)  Synchronous  motions  would  result  again,  in  the 
ulterior  history  of  the  derived  spheroid,  through  the  con- 
tinued action  of  tidal  friction.  This  result,  though  favored 
by  the  existence  of  fluids  on  the  surface,  would  not  be 
permissively  conditioned  upon  it,  since  all  tidal  motions  in 
a  spheroid  whose  constituent  parts  are  not  perfectly  free  to 
move,  are,  by  so  much,  constrained  in  the  direction  opposed 
to  those  motions,  the  tidal  effects  are  delayed  and  the  tidal 
action  becomes  thus  a  constant  effort  to  rotate  the  spheroid 
in  the  direction  of  the  tidal  progress,  that  is,  in  a  direc- 
tion contrary  to  the  normal  rotation  of  the  spheroid.* 

6.  Arrangement  of  Heavier  Matters  on  the  Derived 
Spheroid. — In  all  stages  of  the  derived  spheroid  there 
would  be  a  tendency  of  the  heavier  parts  to  accumulate 
on  the  side  nearest  the  central  attractive  body.  There 
may  be  a  condition  of  matter  in  which  diversified  densities 
have  not  been  attained.  There  is  also,  probably,  a  stage 
of  nebulous  history  in  which  the  Intel-mobility  of  parts 
prevents  adjustment  of  portions  in  accordance  with  densi- 
ties. But  assuredly,  a  time  sooner  or  later  arrives  when 
diversity  of  densities  not  only  exists,  but  the  conditions  are 
such  that  the  positions  of  the  parts  must  be  determined 
by  their  relative  densities.  While  synchronistic  motions 
exist,  there  will  be  two  forces  acting  toward  the  determi- 

*  The  subject  of  tidal  action  will  be  resumed  and  studied  in  greater  detail  in 
connection  with  planetary  evolution. 


138  NEBULAR   LIFE. 

nation  of  those  relative  positions.  One  is  the  central 
attraction  toward  the  centre  of  orbital  motion;  the  other 
is  the  centrifugal  tendency  resulting  from  the  orbital  mo- 
tion. The  nearest  parts  experience  most  of  the  centripe- 
tal tendency,  and  the  remotest  parts,  most  of  the  centrifu- 
gal tendency.  The  centripetal  force  tends  to  bring  the 
denser  parts  to  the  nearer  side,  and  the  centrifugal  force 
tends  to  transfer  them  to  the  remoter  side.  Unless  the 
excess  of  the  centripetal  force  on  the  nearer  side  exactly 
equals  the  excess  of  the  centrifugal  force  on  the  remoter 
side,  the  heavier  parts  must  tend  toward  one  extremity  of 
the  prolate  axis.  Whichever  be  the  side  toward  which  they 
settle,  the  resulting  distribution  of  the  matter  must  consti- 
tute a  resistance  to  the  disturbance  of  synchronistic  motions. 

The  factors  entering  into  a  determination  of  the  ques- 
tion to  which  side  the  heavier  parts  would  tend  are,  the 
mass  of  the  central  body,  the  distance  between  its  centre 
of  gravity  and  that  of  the  derived  spheroid,  the  length  of 
the  prolate  axis  of  the  derived  spheroid  and  the  velocity  of 
motion  in  its  orbit. 

In  any  particular  case,  where  the  mass  of  the  central 
body  and  the  length  of  the  prolate  axis  remain  constant, 
the  relation  of  the  differential  centripetal  and  centrifugal 
forces  to  each  other  will  vary,  on  condition  of  uniform 
angular  velocity  of  rotation,  with  the  distance  between 
the  centres  of  gravity  of  the  two  bodies.  But  the  differ- 
ential centrifugal  tendency,  on  the  conditions  assumed, 
remains  constant.*  On  the  contrary,  since  the  centripetal 

*  The  centrifugal  tendencies  at  the  nearer  and  remoter  poles  of  the  prolate 
axis  being  represented  by  F'  and  F",  and  the  distances  of  these  poles  by  d'  and 
i/",  we  have  for  the  angular  velocity  0,  by  the  principles  of  mechanics,  F"—F' 
—  d"#»— cf'0*  Now  suppose  the  spheroid  to  be  placed  at  a  different  distance 
from  the  central  body,  so  that  d'=  d' ±  nandd"=d"±  n.  Letting/' and/"  rep 
resent  the  centrifugal  tendencies  at  the  poles  of  the  prolate  axis,  in  the  new 
position,  we  have,  for  the  game  angular  velocity  as  before,/''— /'=  (d''±  n)6s  — 
(d'  ±  n)  fl»=  d"V*  -  d'tft-  F"-  P.  Hence  the  differential  centrifugal  tendency 
remains  constant. 


SPHEKATION   OF   RINGS.  139 

force  varies  inversely  as  the  square  of  the  distance,  the 
differential  centripetal  tendency  increases  with  the  distance 
between  the  two  bodies.  Hence  if,  at  any  distance,  the 
differential  centripetal  and  centrifugal  tendencies  are 
equal,  at  a  less  distance  the  centrifugal  would  preponder- 
ate, and  at  a  greater,  the  centripetal  would  preponderate. 
Where  the  orbital  motion  at  different  distances  is  in  con- 
formity with  Kepler's  third  law,  the  angular  velocity,  and 
hence  the  differential  centrifugal  tendency  would  be  in- 
creased with  shortening  of  the  distance;  and  accordingly, 
the  differential  centripetal  and  centrifugal  tendencies 
would  not  diverge  as  rapidly  (with  a  given  rate  of  change 
in  distance),  as  when,  according  to  our  first  supposition, 
the  angular  velocity  remains  constant.* 

7.  Orders  of  Nebuke. — Let  us  remember  that  our 
speculations  thus  far  concern  nebulae;  and  that  the  segre- 
gation of  parts  results  in  a  system  of  nebulous  masses, 
.  each  of  which  in  turn  may  be  destined  to  repeat  the  evo- 
lutions of  the  parent  nebula.  Consider  then,  one  of  these 

*  The  equation  of  differential  centripetal  and  centrifugal  tendencies  presents 
the  following  relation  among  the  values  involved: 
Let  g  =  gravity  at  the  central  body's  surface,  assumed  to  be  a  sphere  without 

rotary  motion. 
d>  and  d"=  distances  from  centre  of  gravity  of  the  central  body  to  the 

nearest  and  remotest  poles  of  the  prolate  axis. 

v'  and  «"=  the  linear  orbital  velocites  respectively  of  these  two  poles. 
R  =  radius  of  central  sphere. 

Then  the  condition  of  eqnal  differential  centripetal  and  centrifugal  tendencies 
gives 


Slr-aF^^Gs-i)' 


U"L 
Also,  since  the  angular  velocity  0  =  — , 


140  NEBULAR   LIFE. 

partial  nebulae.  Though  presenting  but  a  small  disc,  at 
the  enormous  distance  from  which  we  gaze  upon  it,  we 
must  suppose  its  diameter  greater  than  that  of  our  solar 
system.  It  is  still  in  large  part  an  incandescent  vapor. 
There  was  a  time  when  the  matter  of  our  solar  system 
was  one  of  these  partial  nebulas,  or  perhaps  an  original 
growth  which  had  never  attained  larger  dimensions,  or 
perhaps  again,  one  of  the  segregated  masses  of  a  non- 
rotating  nebula.  Many  of  the  stars  in  our  firmament 
represent  other  nebulas  of  the  same  order,  out  of  which 
have  emerged  the  stars  and  the  planetary  systems  which 
probably  circle  around  them.  It  was  the  speculation  of 
Kant,  and  the  original  conception  of  Sir  William  Herschel 
(though  he  did  not  so  distinctly  enunciate  the  agency  of 
rotation)  that  at  periods  incalculably  remote,  an  enormous 
system  of  partial  nebulae  had  issued  from  that  grand  uni- 
versal nebula  which  contained  all  the  matter  of  our  firma- 
ment of  stars  and  planets.  This  firmament,  as  they 
thought,  was  possibly  once  a  nebula,  like  those  other  thou- 
sands of  nebulas  which  we  believe  to  have  advanced  varying 
distances  on  the  way  to  completed  stellation.  Kant  con- 
ceived that  it  performed  then  a  stupendous  gyration  about 
an  axis.  Even  now,  that  gyration  should  be  continued. 
The  idea  is  not  entirely  fanciful;  for  astronomers  have 
shown  that  all  the  stars,  as  a  rule,  are  actually  in  motion; 
and  Maedler  believes  that  he  has  rendered  it  probable  that 
our  sun  has  Alcyone  in  the  Pleiades  for  the  centre  of  its 
orbit,  and  consumes  180  millions  of  years  in  completing  a 
single  revolution.  If  a  nebula  requires  180  millions  of 
years  for  a  single  rotation,  what  change  of  position  could 
we  expect  to  detect  in  the  brief  interval  since  the  con- 
struction of  Sir  William  Herschel's  great  telescope? 

It  must  be  soberly  said,  however,  that  there  is  com- 
paratively little  ground  for  the  opinion  that  our  entire 
firmament  is  now  in  a  state  of  gyration  about  a  common 


SPHERATION   OF    RINGS.  141 

centre.  In  such  case  there  would  be  more  consentaneous- 
ness  in  the  movements  which  have  been  actually  traced 
among  the  fixed  stars.  There  is  no  conceivable  system  of 
relative  positions  and  velocities  about  a  common  centre 
which  would  develop  the  seemingly  sporadic  movements 
which  we  witness.  Undoubtedly  every  star  is  in  motion; 
and  undoubtedly  every  star's  motion  is  in  obedience  to  the 
laws  of  central  forces.  Undoubtedly  the  sun  and  solar 
system  are  moving  majestically  across  the  spaces  which 
separate  star  from  star.  It  is  shown  also  that  many  coup- 
lets and  larger  groups  of  stars  are  physically  connected; 
and  that  most  of  the  stars  in  certain  regions  of  the  heav- 
ens possess  a  common  motion;  but  we  have  not,  as  yet, 
good  inductive  ground  for  affirming  a  common  rotary 
motion  of  our  firmament,  or  its  derivation,  by  the  annula- 
tion  process,  from  a  general  firmamental  nebula.  There 
is  more  ground  for  the  belief  that  each  star  is  the  residual 
centre  of  a  distinct  nebular  mass,  by  whatever  process  iso- 
lated. We  may  therefore  reasonably  proceed  to  contem- 
plate the  evolution  of  a  solar  nebula,  regardless  of  the 
nature  of  its  origin  or  previous  transformations.  This 
brings  us  to  the  question  of  the  primitive  history  of  a 
solar  system. 

But  we  pause  here  in  the  midst  of  our  speculations. 
The  very  firmament  is  careering  in  infinite  space,  while  we 
ponder  on  its  constitution  and  history  or  turn  to  our  ma- 
terial occupations.  Our  comfortable  homes,  while  we  dine 
or  sleep,  are  rolled  through  space  at  the  rate  of  seven  hun- 
dred miles  an  hour  by  the  diurnal  rotation  of  the  earth. 
During  the  same  time  they  are  transported  sixty-eight 
thousand  miles  by  the  movement  of  the  earth  in  its  orbit. 
Then  the  sun,  with  his  entire  family  of  planets,  is  sweep- 
ing through  immensity,  toward  the  constellation  Hercules, 
with  a  velocity  which,  if  equal  to  that  of  Arcturus,  is  two 
hundred  thousand  miles  an  hour.  And  lastly,  there  must 


142  NEBULAR   LIFE. 

be  some  common  motion  of  translation  of  the  whole  inex- 
tricable maze  of  moving  stars,  and  with  a  velocity  to  which 
fancy  may  assign  what  rate  it  pleases  without  restraint 
from  science.  This  mighty  waltz  of  cosmic  dancers  is  joined 
by  the  gauzy  nebulae,  animated  also,  like  our  firmament, 
by  their  own  internal  motions.  In  the  midst  of  this  uni- 
verse of  seething  movements  is  our  appointed  home.  The 
mind  uplifted  in  the  effort  to  contemplate  them  and  grasp 
their  method,  grows  giddy  and  impotent.  How  sublime 
these  activities !  To  what  a  numerous  and  lofty  compan- 
ionship does  our  little  planet  belong !  Hard  it  seems  to 
be  imprisoned  here  while  the  realm  of  the  universe  tempts 
us  to  its  exploration.  How  can  a  human  soul  content 
itself  to  roll  and  whirl  through  space  during  its  mortal 
days,  and  eat  and  sleep  and  trifle,  like  rats  in  a  ship  at  sea, 
without  wondering  where  we  are  and  whither  we  are  bound  ? 


PART  II. 
PLANETOLOGY 


CHAPTEE  I. 
ORIGIN    OF    THE    SOLAR    SYSTEM. 

Theoriarum  vires,  arcta  et  quasi  se  mutuo  sustinente  partium  adaptatione, 
qua,  quasi  in  orbem  cohserent,  firiuautur.*— BACON. 

Erst,  space  was  nebulous. 
It  whirled,  and  in  the  whirl,  the  nebulous  milk 
Broke  into  rifts  and  curdled  into  orbs  — 
Whirled  and  still  curdled,  till  the  azure  rifts 
Severed  and  shored  vast  systems,  all  of  orbs.— DAVID  MASSON. 

I  HAVE  presented,  in  the  preceding  chapters,  some  of 
the  evidences  of  the  wide  diffusion  of  world-stuff 
through  space.  We  have  no  warrant  whatever  for  affirm- 
ing its  diffusion  "through  infinite  space";  nor  can  we 
rationally  speak  of  any  particular  condition  of  this  matter 
at  any  absolute  "beginning."  Nor  can  we  affirm  that  it 
was  distributed  "uniformly";  nor  that  its  tenuity  was 
any  number  of  thousand  times  "greater  than  that  of 
hydrog'en."  It  suffices  to  recognize  the  evidence  that  the 
cosmic  matter  which  we  now  see  aggregated  in  worlds 
existing  in  various  stages  of  development  from  a  conceiv- 
able and  rational  starting  point,  was  once  widely  diffused, 
and  probably  cold;  and  that  by  the  mutual  attractions  of 
particles  and  masses,  much  of  this  matter  became  gathered 
into  aggregations  of  vast  magnitude. 

I  have  also  attempted  to  show  that  the  further  opera- 
tion of  gravity  would  tend  perpetually  to  the  further 
aggregation  of  these  masses,  and  that  their  collisions 
would  result  in  the  development  of  intense  heat.  I  have 

*The  strength  of  theories  is  established  by  their' compact  and  mutually 
sustaining  eoadaptation  of  parts,  by  which  they  cohere  as  in  an  arch. 
10  145 


146  ORIGIN   OF   THE   SOLAR   SYSTEM. 

shown  that  rotary  motion  must  have  been  also  a  result  of 
such  collisions;  and  must  also  have  been  generated  by 
mutual  attractions  without  the  occurrence  of  collision.  I 
have  traced  the  further  consequences  of  the  rotation  of  a 
heated  globe  of  nebulous  matter,  and  have  pointed  out  the 
necessity,  in  some  cases,  of  a  process  of  annulation,  and 
the  subsequent  gathering  of  the  rings  into  spheroidal 
masses  rotating  on  their  axes  and  revolving  in  orbits  about 
the  residual  mass.*  The  process,  as  described,  results  in 
breaking  up  a  great  firmamental  nebula  into  a  large 
number  of  partial  or  solar  nebula;;  and  it  is  one  of  these, 
or  at  least  a  nebula  of  this  order  of  magnitude,  which  we 
are  to  follow  further  in  the  course  of  its  evolution. 

It  is  not  implied  that  all  solar  nebulae  have  been  thus 
derived.  It  cannot  be  doubted  that  many  riebuhe  are  of 
magnitudes  so  small  comparatively  that  they  condense 
directly  into  suns  and  planets.  They  have  never  been  of 
any  higher  order  than  solar  nebulae.  Whatever  its  ante- 
cedent history,  it  is  the  solar  nebula  to  which  attention 
is  now  directed. 

Being  a  nebulous  mass  essentially  identical,  except  as 
to  magnitude,  with  the  firmamental  nebula  which  we  have 
been  considering,  it  is  evident  that  all  its  nebulous  history 
must  be  essentially  such  as  we  have  already  traced.  It 
only  remains,  therefore,  to  continue  to  follow  the  evolution 
in  a  case  in  which  a  nebulous  globe  condenses  directly  to 
the  solar  and  planetary  conditions.  What  needs  to  be 
said  to  make  this  part  of  the  process  plain  to  the  reader 
can  perhaps  be  best  presented  in  the  form  of  a  citation  of 
actual  phenomena  which  find  their  best  explanation  in  a 
nebular  evolution;  and  then  a  discussion  of  the  various 

*  Should  the  reader  feel  interested  in  further  views  on  the  origin  of  clusters 
and  nebulae,  he  may  consult  memoirs  of  Prof.  Stephen  Alexander  in  Gould's 
Astronomical  Journal,  vol.  ii,  1852;  as  also  those  of  Sir  William  Herschel  as 
cited  in  Part  IV,  ch.  iii,  §  2,  of  the  present  work,  and  the  coincident  views  of 
Arago  in  Astronomic  populaire. 


VERIFICATION    OF   THE    NEBULAR   THEORY.          147 

objections  wnich  have  been  urged  against  the  theory  by 
various  classes  of  persons. 

§  1.     VERIFICATION  OP  THE   NEBULAR  THEORY  FROM 
FACTS. 

I.  Observed  Phenomena  of  the  Solar  System  which 
accord  with  the  requirements  of  the  Nebular  Theory. 

A.       DEMONSTRATIVE    PHENOMENA. 
(See  Works  on  Astronomy.) 

1.  The  planets  all  move  in  their  orbits  in  the  same 
direction. 

2.  The  sun  rotates  on  his  axis  in  the  same  direction  as 
the  planets  revolve  in  their  orbits. 

3.  All  the  planets,  except  Uranus  and  probably  Nep- 
tune, rotate  on  their  axes  in  the  same  direction. 

4.  All  the  satellites  revolve  in  their  orbits  in  the  same 
direction,  except  those  of  the  planets  Uranus  and  Nep- 
tune. 

5.  The  moon  rotates  on  its  axis  in  the  same  direction; 
and  no  satellite  is  known  to  rotate  in  the  opposite  direc- 
tion. 

6.  The  planes  of   all  the  planetary  orbits  are  nearly 
coincident. 

7.  The  plane  of  Neptune's  orbit  is  almost  exactly  coin- 
cident with  the  invariable  plane  of  the  solar  system.     (See 
§  3,  1.) 

8.  The  planes  of  all  the  planetary  orbits  in  the  course 
of  their  secular  oscillations  approach  nearly  to  coincidence 
with  the  invariable  plane;  and  the  orbits  of  Venus,  the 
Earth  and   Mars   attain    to   complete    coincidence.      (See 
§3,1.) 

9.  The  planes  of  the  secondary  orbits  are  all  nearly 
coincident  with  the  planes  of  the  equators  of  their  pri- 
maries. 


148  ORIGIN    OF   THE   SOLAR   SYSTEM. 

10.  The  plane  of  the  sun's  equator  is  nearly  coincident 
with  the  invariable  plane  of  the  solar  system. 

11.  The  sun  is  the  centre  of  motion  of  all  the  planets. 

12.  Every  system  of  satellites  has  one  primary  for  its 
centre  of  motion. 

13.  The  orbital  paths  of  the  planets  and  satellites  vary 
but  little  from  circles. 

14.  The   larger  planets    have  the   greater  number  of 
satellites  because  greater  mass  would  prolong  the  period 
of  mobility  of  parts,  and  thus  the  possibility  of  annula- 
tion. 

15.  The  angular,  and  also  the  actual  velocities  of  the 
planets  and    satellites  in   their  orbits   increase   with    the 
decrease  of  their  mean   distances  from  their  centres  of 
attraction. 

16.  The  Saturnian  system  still  retains  an  example  of 
the  ring-condition. 

17.  The  Earth  furnishes  evidence  of  intense  internal 
heat,  and  other   evidences  of   a  general    temperature    in 
ancient  times,  sufficiently  high  to  fuse  rocks  at  the  sur- 
face.    (See  chap.  Ill,  §  1,  1.) 

18.  The  superposition  of  unaltered  sedimentary  rocks 
over  metamorphic  sedimentary  rocks  implies  a  process  of 
cooling.     (See  works  on  Geology.) 

19.  The  animal  and  vegetable  forms  fossilized  in  the 
older  rocks  prove  an  ancient  higher  temperature  for  the 
terrestrial  climates.     (See  Sketches  of  Creation  and  works 
on  Geology.) 

20.  The  oblateness  of  the  other  planets  implies  a  for- 
mer state  of  fluidity  in  them. 

21.  The  crater-like  forms  seen  upon  the  surface  of  the 
moon   indicate    a    former    intensity    of     igneous     action. 
(Chap.  Ill,  §  2,  3.) 

22.  The  absence  of  air  and  water  from  the  moon  indi- 
cates a  state  of  complete  refrigeration.     (Chap.  Ill,  §  2,  5.) 


VERIFICATION    OP   THE    NEBULAR   THEORY.          149 

23.  The  cloud-enveloped  condition  of  Jupiter,  together 
with  some  indications  of   inherent    luminosity,  implies  a 
temperature  higher  than  that  of  the  earth;  and  this  may 
be  supposed  inherited  from  a  past  still  more  highly  heated 
condition.     A  less  advanced  stage  than  that  attained  by 
the  earth  would  be  attributable  to  the  vastly  greater  mass 
of  matter  in  that  planet,  which  would  demand  vastly  more 
time  to  reach  a  cooled  and  habitable  condition.     (Chap. 
Ill,  §  5.) 

24.  The  substances  which  enter  into  the  constitution 
of  the  sun  are  the  same  as  those  in  the  earth.     (See  Young 
on    The  Sun;    Secchi :    Le  Solid;    Schellen :    Spectral 
Analysis,  etc.) 

25.  The  composition  of   meteorites   coming  from   the 
planetary  spaces  is  terrestrial,  and  points  to  the  general 
inference  that  all  the  bodies  occupying  the  planetary  spaces 
have  the  same  composition  as  the  earth  and  the  sun.     (See 
Meunier:  Le  Ciel  Geologique,  and  works  on  meteorites.) 

26.  The  planets  and  satellites  all  move  about  their  cen- 
tral bodies  with  velocities  so  varying  with  the  distance 
that  the  radius  vector  of  each  body  describes  equal  areas 
in  equal  times. 

27.  Our  satellite  always  turns  the  same  side  toward  the 
earth;  and  so  far  as  we  know,  all  the  satellites  of  our  sys- 
tem turn  always  the  same  side  toward  their  primaries. 

28.  The  sun  still  exists  in  a  nebulous  condition  so  far 
as  exposed  to  our  inspection. 

B.       PHENOMENA    PROBABLY    CONFIRMATORY. 

29.  The  period  of  rotation  of  Saturn's  rings  is  less  than 
the  axial  rotation  of  the  planet. 

30.  The  orbital  velocities  of  the  planets  conform  to  the 
third  law  of  Kepler  instead  of  being  in  the  ratio  of  the 
squares  of  the  mean  distances  from  the  sun.     (See  §  2, 
Objection  4.) 


150  ORIGIN    OF   THE    SOLAR    SYSTEM. 

31.  The  ratio  of  the  radii  of  gyration  of  the  successive 
spheroids  in   the  development   of  the   Jovian  system,  to 
the  actual  mean  distances  of  the  Jovian  satellites,  is  less 
than  the  corresponding   ratios  in   the   original   planetary 
spheroids  to  the  actual  mean  distances  of  the  planets  from 
the  sun. 

32.  The  rate  of  axial  rotation  as  we  recede  from  the 
centre  of  motion  of  the  system  toward  the  periphery  is 
increasingly  more  rapid  (p.  165).     The  only  exception  is 
Jupiter,  which  rotates  36°  an  hour,  while  Saturn  rotates 
only  34°.5  an  hour.     (See  Part  I,  ch.  ii,  §  4,  2.) 

II.  Observed  Phenomena  not  belonging  to  the  Solar 
System  which  accord  loith  the  requirements  of  the  Nebular 
Theory.  (See  Part  I,  ch.  ii.) 

33.  The   nebulre   and    other  cosmic   bodies  exist   in   a 
nebulous  state. 

34.  The    ring    condition     actually    exists    in    certain 
nebulae. 

35.  Spiral  and  other  nebulous  forms  indicate  a  state  of 
rotation. 

We  may  cite  in  addition  the  brilliant  experiment  of 
Plateau.* 

All  the  foregoing  phenomena  observable  within  the  solar 
system  are,  at  least  to  the  28th, f  so  obviously  conform- 
able to  the  requirements  of  the  nebular  theory  that  prob- 
ably no  reasonable  person  will  maintain  that  they  present 
any  difficulties.  Now  what  must  be  said  in  view  of  such  a 
catalogue  of  coincidences?  They  show  at  least,  that  all 
parts  of  our  system  must  have  had  a  common  origin  and  a 

*  J.  Plateau :  Memolre  sur  les  phenomenes  qite  prisente  une  masse  liquide  libre 
et  soustraite  a  I'aclion  de  la  pesanteur,  Nouveaux  inemoires  de  1' Academic  de 
Bruxelles,  xvi.  1843,  translation,  Experimental  and  Theoretical  Researches  on  the 
Figures  of  Equilibrium  of  a  Liquid  Mats  Withdrawn  frcm  the  Action  of 
Gravity,  etc.,  Smithsonian  Reports,  1863. 

t  Prof.  Stephen  Alexander  enumerates  62  "consistencies"  or  confirmations 
of  the  nebular  theory  (Smithsonian  Contributions  xxi,  Art.  I,  pp.  80-91). 


VERIFICATION   OF   THE    NEBULAR   THEORY.          151 

common  history.  If  our  earth  has  had  a  cosmic  history, 
then  that  history  involved  all  the  other  bodies  of  our  system. 
Unless  we  choose  to  abandon  all  scientific  method,  and 
dogmatically  assert  that  each  world  is  the  product  of 
immediate  creation,  and  deny  that  the  plan  which  embraces 
their  forms  and  movements  shows  any  physical  relation 
among  them,  we  must  seek  for  a  theory  of  their  past 
history  which  will  coincide  in  all  these  twenty -eight  par- 
ticulars with  the  facts  of  observation.  But  a  physical 
relation  exists  among  all  the  parts  of  the  solar  system  in 
human  times;  they  are  acting  mutually  upon  each  other; 
new  positions  and  conditions  are  daily  arising  out  of  these 
mutual  actions.  We  have  seen  a  brief  chapter  of  cosmical 
history  enacted  during  the  period  of  our  observations;  and 
the  denial  that  this  history  stretches  back  into  prehistoric 
and  remoter  times  is  a  folly  only  equalled  by  that  of  a  man 
who  should  stand  on  the  banks  of  the  Mississippi  at  New 
Orleans,  and  declare  that  the  stream  had  no  existence 
northward  beyond  the  range  of  his  vision.  The  parts  of 
the  solar  system  are  physically  connected  in  human  times; 
and  he  who  would  deny  that  the  history  of  such  connection 
stretches  into  a  remote  past  is  incapable  of  reasoning  on 
the  subject. 

Now,  if  the  real  history  whose  outcome  we  look  upon 
is  a  history  of  physical  actions  and  reactions,  what  concep- 
tion can  be  formed  of  the  particular  nature  of  that  history 
which  will  be  more  conformable  to  the  leading  facts  of 
observation  than  the  conception  of  an  original  nebula, 
rotating  and  cooling,  and  evolving  progressively  the  inci- 
dents of  such  a  process  ?  With  so  extended  a  catalogue 
of  coincidences,  a  mere  hypothesis  ought  to  be  regarded 
as  a  highly  probable  representation  of  the  truth;  unless 
some  grand  phenomenon  remains  to  be  accounted  for,  or 
some  strictly  crucial  test  dissipates  the  accumulated  prob- 
ability in  its  favor. 


152  ORIGIN    OF  THE   SOLAR   SYSTEM. 

I  hear  it  said  that  these  grandly  outlined  events  are 
only  a  dream  —  a  poetic  creation,  without  the  possibility 
of  a  demonstration.  Well,  if  no  more  could  be  said,  I 
am  prepossessed  by  them,  as  the  best  and  most  plausible 
conjectures  which  could  be  made  by  the  wisest  of  men. 
Until  some  objector  can  put  forth  a  more  probable  concep- 
tion of  that  past  history  which  has  been  so  real,  I  deem  it 
wise  to  pay  respect  to  a  conception  which  has  been  grow- 
ing in  esteem  for  three  quarters  of  a  century.  Let  it  be  a 
mere  hypothesis;  it  may  be  one  ripened  into  an  imperish- 
able doctrine.  Gravitation  was  a  mere  hypothesis  once  — 
and  once  even  an  abandoned  hypothesis.  That  the  planets 
move  in  ellipses  was  Kepler's  hypothesis;  but  now  it  is 
demonstrated.  Is  it  said,  the  nebular  hypothesis  cannot 
be  demonstrated?  It  is  all  but  demonstrated  to-day;  and 
he  who  doubts  is  more  credulous  than  he  who  believes.  It 
is  all  but  demonstrated  by  the  three  dozen  coincidences 
which  I  have  enumerated.  And  it  is  all  but  demonstrated 
by  the  rigorous  processes  of  mathematics  which  so  long 
since  gave  a  rational  basis  to  Kepler's  laws. 

Yet,  in  the  presence  of  so  many  coincidences  and  con- 
firmations; with  the  great  weight  of  almost  unanimous 
scientific  opinion  for  an  indorsement,  we  find  such  a  judg- 
ment as  the  following  on  record  in  a  work  which  is  still 
recent:  "We  are  obliged  to  conclude  that  the  nebular 
theory  lacks  all  the  elements  of  credibility.  It  is  at  vari- 
ance with  astronomical  facts.  It  is  destitute  of  philo- 
sophical consistency.  It  assumes  everything  that  ought 
to  be  demonstrated.  It  deals  in  glittering  generalities 
where  it  ought  to  go  into  minute  details.  It  ignores  the 
mathematical  relations  of  forces  and  effects.  In  fine,  its 
data  are  intangible,  incongruous  and  impertinent  to  its  con- 
clusions. Never  in  the  history  of  science  was  theory  more 
pretentious.  Never  did  theory  less  justify  its  preten- 


OBJECTIONS   FROM    PLANETARY    MOTIONS.  153 

sions."*  This  language  is  emphatic  and  unreserved. 
Every  word  deserves  to  be  italicised.  This  is  the  daring 
indictment  drawn  up  against  the  good  judgment  of  such 
astronomers  and  physicists  as  Laplace,  Sir  John  Herschel, 
Helmholtz,  Mayer,  Tyndall,  Sir  W.  Thomson,  Clerk  Max- 
well, Clifford,  Croll,  Huggins,  Lockyer,  Arago,  Oersted, 
Becquerel,  S.  C.  Walker,  Benjamin  Peirce,  B.  A.  Gould, 
D.  Kirkwood,  J.  C.  Watson,  G.  Hinrichs,  D.  Trowbridge, 
S.  Newcomb,  C.  E.  Young,  J.  E.  Hilgard,  Joseph  Leconte 
and  a  host  of  other  names  of  similar  authority  in  these 
and  other  departments  of  natural  science.  How  superior 
must  be  the  knowledge  and  the  penetration  of  the  indi- 
vidual who  could  bring  such  an  indictment  against  such 
an  array  of  honored  names.  And  how  clear  and  demon- 
strative the  apprehension  of  the  grounds  of  an  indictment 
presented  with  such  unruffled  assurance  of  infallibility. 

§  2.   OBJECTIONS  BASED  ON  RELATIONS  OF  PLANETARY 
MOTIONS. 

Let  us  now  examine  the  phenomena  which  by  one  and 
another  have  been  cited  as  incompatible  with  the  nebular 
theory. 

1.  Retrograde  Motions.^ — The  satellites  of  Uranus  re- 
volve in  a  plane  which  makes  an  angle  of  98°  with  the  plane 
of  the  ecliptic.  That  is,  the  system  is  tilted  up  until  it  is 
8°  beyond  a  right  angle  with  the  ecliptic,  and  the  satellites 
thus  have  an  apparent  retrograde  motion.  Similarly,  the 

*  Rev.  W.  Slaughter:  The  Modern  Genesis  p.  290.  We  might  offset  this  bold 
arraignment  by  the  following  passage  from  an  authority  of  high  and  recognized 
standing  as  a  logician:  ''There  is  thus  in  Laplace's  theory,"  says  John  Stuart 
Mill,  "nothing hypothetical;  it  is  an  example  of  legitimate  reasoning  from  a 
present  effect  to  its  past  cause,  according  to  the  known  laws  of  that  cause;  it 
assumes  nothing  more  than  that  objects  which  really  exist,  obey  the  laws  which 
are  known  to  be  obeyed  by  all  terrestrial  objects  resembling  them  "  (System  of 
Logic,  Am.  ed.,  p.  299.) 

+  M.  Faye,  Comptes  Rendus,  xc,  pp.  566-71,  March,  1880;  Rev.  W.  B.  Slaugh- 
ter: The  Modern  Genesis,  103-109. 


154  ORIGIN   OF  THE   SOLAR   SYSTEM. 

plane  of  Neptune's  satellite  is  tilted  over  145°,  so  that  it 
seems  to  have  a  retrograde  motion  in  an  orbit  inclined  35° 
to  the  plane  of  the  ecliptic.  Now,  nothing  is  more  natu- 
ral than  to  suppose  that  a  partial  inversion  of  these  sys- 
tems has  taken  place.  These  inclinations,  in  fact,  are 
only  extreme  cases  of  the  inclination  which  characterizes 
all  the  orbital  and  equatorial  planes  of  our  system.  The 
satellites  of  Saturn  have  generally  an  inclination  of  28°, 
and  one  of  the  Asteroids  has  an  inclination  of  nearly  35°. 

(1.)  It  is  entirely  conceivable  that  both  the  Uranian 
and  Neptunian  systems  should  have  suffered  an  overturn 
through  the  influence  of  some  powerfully  attracting  body 
passing  in  the  neighborhood.  If  this  occurred  before  the 
planetary  nebula  had  commenced  annulation,  then  the 
motions  of  its  later-formed  satellites  would  conform  to  the 
plane  of  the  planetary  rotations.  If  it  occurred  after  the 
satellites  were  formed,  their  orbits  might  depart  very  far 
from  the  equatorial  plane  of  the  planet.  It  is  even  con- 
ceivable, in  this  case,  that  the  planet's  rotary  motion 
might  be  direct  while  the  orbital  motions  of  the  satellites 
are  retrograde.  The  influence  of  such  disturbing  body 
may  also  have  been  felt  bv  the  Saturnian  system,  which 
shows  an  extraordinary  inclination,  while  the  planets  suc- 
cessively more  remote  have  been  successively  more  dis- 
turbed. 

The  accompanying  figure  (Figure  33)  will  illustrate  a 
possible  method  of  the  overturn  of  a  system  after  the 
formation  of  the  satellites.  It  represents  a  planet  in  its 
orbit,  and  surrounded  by  the  orbit  of  one  of  its  satellites. 
The  latter  orbit  is  originally  coincident  with  the  plane  of 
the  planetary  orbit  as  shown  in  B  N2  A  N.  But  suppose 
when  the  satellite  is  at  A,  an  attractive  influence  to  be 
felt  from  the  direction  C  A;  one  component  of  this  force 
would  act  in  the  direction  A  G,  in  the  plane  of  the  orbit, 
and  would  not  alter  the  inclination  of  the  orbit;  but  the 


OBJECTIONS   FEOM   PLANETARY   MOTIONS.  155 

other  would  act  at  right  angles  with  this,  in  the  direction 
A  F,  and  would  tend  to  carry  A  toward  F,  but  the  attrac- 
tion of  the  planet  would  bring  A  toward  the  position  A'. 
The  satellite  would  pass  on  in  its  orbit,  but  upon  its 
return  to  the  vicinity  of  the  position  A,  a  further  impulse 
would  be  felt.  This  would  be  repeated  again  and  again, 


FIG.  34.  INVERSION  OP  THE  ORBIT  or  A  SATELLITE. 

as  long  as  the  disturbing  body  should  remain  in  the  same 
general  direction.  It  is  true  that  the  satellite  would  be 
attracted  throughout  its  whole  course,  and  at  B  the  effect 
would  be  a  partial  restoration  of  the  original  position  of 
the  orbit;  but  the  influence  at  B  would  be  less  than  at  A, 


156  ORIGIN    OF   THE   SOLAR   SYSTEM. 

because  its  distance  from  the  disturbing  body  is  greater; 
and  hence  the  residual  effect  upon  A  would  be  due  to  the 
difference  of  the  attractions  in  the  two  positions  A  and  B. 

It  is  necessary  to  trace  this  effect  somewhat  farther. 
Had  the  satellite  no  inertia,  the  disturbing  influence  would 
turn  its  orbit  only  so  far  as  to  bring  the  plane  into  coinci- 
dence with  the  direction  of  the  influence  C'  A'  B'.  But 
the  momentum  acquired  will  carry  the  satellite  beyond 
that  point.  If  the  influence  still  persists,  the  orbit  will 
return  and  will  thereafter  oscillate  slightly  on  both  sides 
of  the  plane  of  coincidence.  But  if  the  influence  dis- 
appears, or  if  an  influence  from  another  direction  D  A' 
arises,  the  motion  of  the  orbit  may  continue  until  its  angle 
with  the  plane  of  the  planetary  orbit  exceeds  a  right  angle 
by  any  amount. 

Now,  suppose,  before  the  satellite's  orbit  has  been 
changed  in  position,  an  observer  on  the  earth  looking 
from  the  direction  E,  sees  the  satellite  at  B,  moving  in  the 
direction  of  the  arrow;  call  this  direct  motion.  But  sup- 
pose that  afterward,  when  the  orbit  has  been  tilted  so  that 
the  satellite  on  its  passage  through  the  point  A"  nearest 
the  earth  shall  again  be  seen  from  the  direction  E,  it  is 
evident  that  its  apparent  motion  (in  the  direction  from  the 
node  N  to  the  position  A")  will  be  the  reverse  of  its 
former  motion.  This  would  be  retrograde.  But  the 
satellite  has  continued  to  revolve  in  the  same  orbit  and  in 
the  same  direction,  that  is  from  the  corresponding  posi- 
tions B,  B'  and  B"  toward  the  node  N,  and  from  N  toward 
A,  A'  and  A",  which  represent  the  same  point  in  different 
positions  of  the  orbit 

One  thing  more;  the  action  of  the  disturbing  force  is 
not  likely  to  be  exerted  only  in  a  direction  at  right  angles 
with  the  line  joining  the  nodes  N  and  N2,  of  the  satellite's 
orbit.  One  of  the  effects,  therefore,  will  be  to  wrench  the 
orbit  out  of  its  position;  that  is,  to  change  the  position  of 


OBJECTIONS    FROM    PLANETARY   MOTIONS.  157 

the  hinge-line  N  N2  on  which  it  turns  in  suffering  a  change 
of  inclination.  Or,  in  astronomical  language,  the  longi- 
tude of  the  ascending  node  N  would  be  changed;  and 
when  once  a  motion  from  its  primitive  position  should  be 
begun,  nothing  but  an  exact  equilibrating  force  would 
ever  stop  it.  Thus  the  longitudes  of  the  nodes  of  all  the 
orbits  of  our  system  are  changing  their  positions.  A 
similar  action  would  change  the  position  of  the  apsides  in 
reference  to  the  nodes. 

(2.)  I  have  already  indicated  (p.  120)  another  possible 
cause  of  such  an  irregularity,  in  the  coalescence  of  the  two 
or  more  spheroids  into  which  a  nebulous  ring  may  have 
been  separated.  If  the  resultant  planet,  by  the  collision 
of  these  partial  masses,  has  had  its  axis  tilted  over,  its 
whole  system  of  satellites  must  be  correspondingly  tilted. 

(3.)  In  discussing  the  direction  and  velocity  of  rotation 
acquired  by  a  derived  nebulous  spheroid,  I  have  pointed 
out  the  conditions  under  which  certain  relations  of  density, 
distance  from  the  centre  of  the  nebular  mass,  breadth  of 
ring  and  velocity  would  result  in  retrograde  motion.  Such 
motion  would  be  a  normal  phase  in  the  earlier  stages  of 
the  evolution  of  a  nebula  of  a  certain  magnitude.  It  might 
seem,  therefore,  that  no  occasion  exists  for  seeking  further 
for  the  cause  of  retrograde  motions  in  our  system.  But  it 
must  be  borne  in  mind  that  the  rotations  in  the  Uranian 
and  Neptunian  systems  are  not  completely  retrograde,  but 
lie  in  planes  having  high  angles  with  the  plane  of  the 
solar  system.  That  of  the  Uranian  system  is,  indeed,  but 
little  less  than  a  right  angle.  But  the  cause  here  referred 
to  would  produce  retrograde  motion  very  nearly  in  the 
plane  of  the  solar  equator.  For  this  reason  I  have  not 
placed  this  explanation  in  the  front.  There  is  room  to 
suppose  that  our  solar  nebula  was  not  of  such  magnitude 
as  to  develop  retrograde  rotations  in  its  earlier  stages;  and 
that  the  partial  retrograde  motions  which  we  witness  are 


158  ORIGIN    OF   THE   SOLAR    SYS1EM. 

due  to  the  operation  of  some  other  cause.  The  condition 
of  things  seems  very  strongly  to  suggest  the  action  of 
some  overturning  influence  which  might  cease  with  any 
assignable  degree  of  inclination. 

(4.)  M.  Faye,  who  accepts  in  its  general  features  a 
nebular  history  for  our  solar  system,  has  presented  a 
modification  of  the  theory  of  Laplace,*  in  which  he 
expresses  the  opinion  that  retrograde  motions  would  nor- 
mally prevail  in  the  earlier  stages  of  the  evolution,  and 
direct  motions  in  the  later.  These  views,  as  well  as  the 
similar  ones  of  Professor  Hinrichs,  are  cited  on  a  previous 
page.  It  will  be  noticed,  however,  that  their  theories 
require  the  primitive  retrograde  motions  to  take  place 
nearly  in  the  common  plane  of  the  solar  system.  The 
same  objection  therefore  rests  against  them  as  against  the 
theory  which  connects  direct  rotations  with  increased 
density  of  the  nebula. 

It  may  never  become  possible  to  demonstrate  by  which 
of  the  foregoing  or  other  means  a  retrograde  motion 
became  established  in  the  remoter  parts  of  the  system. 
However,  unless  our  reasoning  is  entirely  at  fault,  it 
appears  that  more  than  one  possible  means  has  existed  for 
producing  retrograde  rotations  in  one  part  of  the  system, 
and  direct  rotations  in  another.  The  state  of  the  facts  is 
such,  at  least,  that  the  existence  of  retrograde  motions  in 
the  remoter  regions  cannot  reasonably  be  assumed  as  a 
fatal  or  even  a  damaging  circumstance  in  nebular  cosmol- 
ogy- 

2.  The  Periodic,  Times  of  the  planets  are  longer  than 
the  Nebular  Theory  attows.-\  —  The  periodic  times  are  of 
course  inversely  proportional  to  the  angular  velocities; 
but,  as  before  stated  (p.  109)  the  angular  velocities  are 

*M.  Faye,  Comptes  Renting,  xc,  637,  March  22,  1880. 

t  D.  Trowbridge,  Amer.  Jour.  Sci.  II,  xxxviii,  3,  4;  Rev.  W.  B.  Slaughter: 
The  Modern  Genesis^  ch.  v. 


OBJECTIONS    FROM    PLANETARY    MOTIONS.  159 

inversely  proportional  to  the  squares  of  the  radii  vectores. 
That  is,  the  time  of  rotation  of  the  nebulous  spheroid 
would  be  proportional  to  the  square  of  its  equatorial 
radius.  But,  by  Kepler's  third  law,  the  actual  periodic 
times  of  the  planets  are  proportional  to  the  square  roots 
of  the  cubes  of  their  mean  distances  from  the  sun.*  The 
periodic  times  of  the  planets  are  therefore  greater  than 
the  theory  allows. 

Now,  I  think  it  may  be  shown  that  such  a  lengthening 
of  the  periodic  times  is  exactly  what  the  theory  requires. 

(1.)  Let  A,  Figure  35,  be  the  last  formed  planet  at  any 
epoch,  revolving  about  the  solar  nebula  in  such  an  orbit 
and  with  such  a  period  as  would  be  required  by  the  nebular 
theory.  Let  C  D  E  represent  the  outer  periphery  of  the 

*  That  is,  while  the  nebular  theory  requires 

6   :    6'  ::  r'a   :   r"1  (p.  109), 

or  what  is  equivalent,  t  :  t'  ::  T*  :  r'a, 

the  actual  motions  of  the  planets  give,  by  Kepler's  third  law, 

<3   :   f*  ::  r3    :   r'3, 

or  t  :    t'  ::  ra    :   P'a' 

t  and  V  being  the  times  of  revolution  of  the  nebulous  disc  in  two  different  states 
of  contraction,  and  therefore  the  theoretical  periodic  times  of  two  planets  result- 
ing from  rings  detached  in  those  states,  and  r  and  r'  the  radius  vector  in  the  two 
states,  or  of  the  two  corresponding  planets.  Now,  if  t'  is  less  than  t,  then  r'  is 
less  than  ?•,  and  the  ratio  r2  :  r'"1  is  greater  than  the  ratio  ra  :  r'a  ;  which 
means  that  t'  when  used  for  the  periodic  time  of  a  planet,  is  greater  than  t'  when 
used  to  express  the  time  of  rotation  of  the  nebulous  spheroid  when  having  a 
radius  r'.  Each  planet,  therefore,  moves  too  slowly  in  reference  to  planets 
exterior  to  it.  In  other  words,  the  progressive  acceleration  has  been  less  than  is 
required  by  the  principle  of  equal  areas. 

Professor  Hinrichs  has  attempted  to  show  analytically  that  the  nebular 
theory  involves  a  passage  from  the  primitive  velocity  into.  the.  rate  of  motion 
expressed  by  Kepler's  third  law  (Amer.  Jour.  Set.  II,  xxxix,  140-1). 

It  is  an  error  of  some  of  the  critics  of  the  nebular  theory  to  assume  that  the 
oblatencss  is  proportional  to  the  angular  velocity,  regardless  of  the  value  of  the 
radius  of  rotation.  Oblateness  depends  on  centrifugal  tendency,  and  this  varies 
directly  as  the  product  of  the  equatorial  radius  of  the  spheroid  into  the  square 
of  the  angular  velocity,  or,  in  other  terms,  directly  as  the  square  of  the  linear 
velocity  and  inversely  as  the  equatorial  radius.  Rev.  Mr.  Slaughter  in  proving 
that  the  observed  rotational  velocity  of  Neptune  is  too  small  to  have  produced  a 
ring-making  degree  of  oblateness  when  the  nebulous  spheroid  extended  to 
Neptune,  compares  only  angular  velocities  (The  New  Genesis,  85-87).  The 
same  error  is  repeated  in  reference  to  the  other  planets. 


160  ORIGIN    OF   THE    SOLAR   SYSTEM. 

residual  central  mass  at  this  time.  Its  centre  of  gravity 
being  at  S,  the  attraction  of  the  whole  mass  constitutes 
the  central  force  which  determines  the  velocity  of  A  in  its 
orbit.  In  process  of  time  another  ring  is  detached,  which 
gathers  itself  into  another  planet  B  or  B'.  The  residual 
nebula  is  now  shrunken  in  volume  to  the  periphery  F  G  H, 
and  is  diminished  in  mass  by  the  whole  amount  of  the 


FIG  35.— PROCESS   op   LENGTHEM.NU    THE    PERIODIC   TIME,  AND 
ACQUIRING  AN  ELLIPTIC  ORBIT. 

planet  B.  The  mass  B  no  longer  constitutes  a  part  of  the 
mass  whose  attraction  determines  the  velocity  of  A.  The 
mass  B,  in  certain  situations  accelerates  that  velocity,  and 
in  others,  retards  it.  Its  influence  has  become  practically 
null.  But  now  the  diminished  mass  whose  centre  of 
gravity  is  at  S  exerts  a  diminished  centripetal  force  on  A. 


OBJECTIONS   FROM    PLANETARY    MOTIONS.  161 

The  planet  A,  therefore,  must  recede  from  S,  and  move 
with  diminished  velocity  in  order  that  a  diminished  centrif- 
ugal force  may  still  equilibrate  the  diminished  centripetal 
force.  It  is  perfectly  obvious  that  the  central  mass  which 
determines  a  certain  velocity  in  a  circum-rotating  body, 
cannot  determine  an  equal  velocity  when  its  mass  is  dimin- 
nished  by  the  separation  of  another  planet;  and  it  is 
equally  evident  that  the  separated  planet  can  contribute 
nothing  permanently  to  the  preservation  of  the  former 
velocity  of  rotation. 

It  must  be  remembered,  however,  that  a  resisting  me- 
dium would  neutralize  a  portion  of  the  centrifugal  tend- 
ency of  the  planet  A,  and  thus  slacken  its  motion  without 
the  necessity  of  a  retreat  from  S.  If  there  were  no  indi- 
cation that  such  retreat  has  taken  place,  we  would  be  at 
liberty  to  assume  that  the  loss  of  centrifugal  force  by 
ethereal  resistance  had  been  just  equal  to  the  loss  of 
centripetal  force  by  diminution  of  the  mass  S.  But  I 
think  it  will  soon  appear  that  these  two  influences  were 
not.  equal. 

(2.)  It  seems  probable  that  a  most  important  influence 
was  exerted  upon  the  behavior  of  the  spheroid  by  the 
enormous  increase  of  density  toward  the  centre.  I  have 
already  directed  attention  in  a  general  way  to  the  neces- 
sary existence  of  such  increase  of  density,  but  we  are 
able  to  adduce  the  results  of  some  calculations  in  reference 
to  the  density  of  the  solar  nebula.*  If  we  assume  that 
the  oblateness  of  the  spheroid  remained  nearly  the  same 
throughout  the  history  of  planet-making,  and  that  in  all 
its  parts  the  centrifugal  force  was  equal  to  the  force  of 
gravity,  the  following  table  will  show  the  densities  of  the 
equatorial  portions  at  the  time  of  the  disengagement  of 
the  several  planetary  rings: 

*  D.  Trowbridge,  Arner.  Jour.  Sci.,  II,  xxxviii,  353-4,  Nov.,  1864. 
11 


162  ORIGIX    OF   THE   SOLAR   SYSTEM. 

Mercury 27.10000000 

Venus 3.10700000 

Earth 1.00000000 

Mars 0.28440000 

Asteroids 0.01976000 

Jupiter .' 0.00311300 

Saturn 0.00037310 

Uranus 0.00003234 

Neptune 0.00001485 

The  calculation  shows  that  the  density  of  the  Mercurial 
ring  was  1,825,000  times  as  great  as  the  density  at  the 
outer  periphery  of  the  Neptunian  ring.*  As  the  disen- 
gagement of  planetary  rings  continually  diminished  the 
nebular  mass,  it  diminished  the  power  of  the  central 
attraction  to  maintain  its  high  primitive  density  or  ten- 
sion, and  we  must  therefore  conclude  that  before  the 
abandonment  of  the  Neptunian  ring  the  density  at  the 
distance  of  each  of  the  future  planets  was  greater  than 
the  above  table  shows. 

The  same  general  conclusion  is  indicated  by  a  calcu- 
lation of  another  sort,  which  shows  that  the  radius  of 
gyration  of  the  solar  nebula  always  bore  a  small  ratio  to 
the  equatorial  radius.  In  the  following  table  the  first 
column  of  numbers  gives  the  leng'th  of  the  radius  of 
gyration  of  the  nebular  spheroid  at  the  time  of  sepa- 
ration of  each  of  the  planetary  rings,  and  the  second 
column  gives  the  equatorial  radius  of  the  spheroid  at 
the  same  epochs,  assuming  this  to  have  been  the  same 
as  the  mean  planetary  distances  at  the  present  time. 


*  It  results  from  an  in 
ity  of  the  sun's  interior, 
hydrogen  or  atmospheric 
value  ranging  from  7.11, 
third  greater  than  the  de 
63,64).  According  to  a 


estigation  made  by  J.  H.  Lane  on  the  necessary  dens- 
n  the  supposition  that  it  is  composed  of  gases  like 
r,  that  such  density  at  the  interior  must  be  of  some 
bout  the  density  of  cast  iron,  to  28.16,  which  is  onc- 
sity  of  platinum  (J.  H.  Lane,  Amer.  Jour.  Set.,  II,  1, 
w  formulated  by  Legendrc  and  adopted  by  Laplace, 


the  earth's  density,  which  is  2.55  at  the  surface,  is  8.5  at  the  mid-radius  and  11.3 
at  the  centre. 


OBJECTIONS   FROM   PLANETARY   MOTIONS.  163 

The  mean  distance  of  the  earth  is  taken  at  92£  millions  of 
miles.* 

RADIUS   OF   GYRATIOX.      EQUATORIAL   RADIUS. 

Mercury 454,000  37,750,000 

Venus 725,600  66,750,000 

Earth 925,200  92,333,000 

Mars 1,269,000  141,000,000 

Asteroids 2,145,000  254,000,000 

Jupiter    3,187,000  480,000,000 

Saturn 5,022.000  881,000,000 

Uranus  8,480,000  1,771,000.000 

Neptune 11,870,000  2,775,000,000 

This  table  shows  that  the  radius  of  gyration  was  always 
remarkably  short  compared  with  the  equatorial  radius  of 
the  spheroid.  As  the  radius  of  gyration  is  the  distance 
of  the  centre  of  inertia  from  the  axis  of  rotation,  it  fol- 
lows that  the  greater  portion  of  the  mass  of  the  nebula 
was  always  condensed  about  the  centre.  It  is  probable 
that  when  the  Neptunian  ring  was  abandoned,  more  than 
half  the  entire  mass  of  the  solar  nebula  was  within  the 
limits  of  the  future  orbit  of  the  earth,  and  the  greater 
part  of  this  portion  was  within  the  future  orbit  of 
Mercury. 

To  make  the  supposed  facts  clearly  intelligible,  let  S, 
Figure  36,  represent  the  centre  of  the  nebulous  spheroid 
at  the  time  of  the  disengagement  of  the  Neptunian  ring, 
S  N  the  equatorial  radius,  S  K  the  radius  of  gyration,  S  M 
the  radius  of  the  future  orbit  of  Mercury,  and  S  E  that 
of  the  earth.  Now  S  K  being  represented  by  a  quarter  of 
an  inch,  S  M  is  3.2  times  as  great,  S  E,  7.7  times  as  great, 
and  SN  should  be  23.4  times  as  great.  That  is,  SN 
should  be  represented  by  58^  inches.  Or,  if  S  N  is  repre- 
sented by  six  inches,  S  K  should  be  one-fortieth  of  an  inch. 

*  Compare  D.  Trowbridge,  Amer.  Jour.  ScL,  II,  xxxvii,  352-3;  D.  Kirkwood, 
Amer.  Jour.  Sci.,  II,  xxxix,  66-9;  S.  Alexander,  Proc.  Amer.  Assoc.,  Cincin- 
nati, 1851  (oral  discussion  only). 


164  ORIGIN    OF   THE    SOLAR    SYSTEM. 


Now  let  us  imagine  the  sphere  whose 
radius  is  S  N  rotating  about  an  axis 
passing  through  S.  The  point  K  is 
that  at  which,  if  an  opposing  force 
equal  to  the  energy  of  rotation  should 
be  applied,  it  would  completely  arrest 
the  rotation  (supposing  the  spheroid 
rigid)  without  producing  any  ten- 
dency of  the  end  S,  of  the  radius,  to 
move  out  of  its  place.  Now,  consid- 
ering that  the  point  K  is  only  one 
two  hundred  and  thirty-fourth  of  the 
distance  from  S  to  N,  we  may  easily 
imagine  to  what  extent  the  mass  of 
the  matter  must  be  gathered  about 
the  centre  S. 

What  then  may  be  inferred  from 
such  relations  of  density  ?  It  seems 
manifest  that  the  exterior  portions 
must  contract  much  more  rapidly 
than  the  interior.  Their  velocity 
would,  therefore,  tend  to  a  more 
rapid  acceleration.  As  the  mass  was 
not  rigid,  the  exterior  parts  must 
have  actually  experienced  a  more 
rapid  acceleration.  Now,  if  an  outer 
planet  revolves  with  a  greater  veloc- 
ity in  reference  to  the  next  interior, 
the  ratio  of  their  periodic  times  is 
brought  nearer  to  a  ratio  of  equality 
than  before;  and  this  is  in  the  direc- 
tion toward  the  rate  required  by 
Kepler's  third  law;  and  we  are  per- 

FIG.  36.  —  ILLUSTRATING  INCREASE  OP  DENSITY 
TOWAHD  THE  CENTRE  OP  THE  NEBULOUS 
SPHEROID. 


OBJECTIONS   FROM   PLANETARY   MOTIONS.  165 

fectly  at  liberty  to  assume  that  the  cause  here  considered 
is  the  one  which  brought  the  periodic  times  to  the  relation 
expressed  by  that  law.* 

But  it  may  be  further  suggested,  that  if  the  central 
parts  acquired  most  of  their  condensation  before  rotation 
began,  they  may  be  in  a  state  of  slower  rotation  than  the 
more  external  parts.  In  this  case,  the  friction  of  the 
rapidly  accelerating  exterior  portions  upon  the  interior 
portion,  would  prevent  the  accelerating  tendency  from 
being  fully  realized,  and  thus  the  planetary  rings,  and  the 
planets  themselves,  would  have  a  slower  orbital  motion 
than  would  be  indicated  by  the  volume  of  the  shrinkage, 
and  might  fall  into  conformity  with  Kepler's  third  law. 
Finally,  each  process  of  annulation  removed  from  the 
spheroid  its  most  rapidly  rotating  portion,  and  left  only  a 
slower  rotating  remainder.  The  sun,  which  remains,  may 
be  conceived  as  having  undergone  many  thousand  times 
less  contraction  since  rotation  began,  than  the  matter 
about  the  equator  of  the  primitive  spheroid. j-  It  is  the 
remnant  of  an  original  nuclear  portion,  and  has  acquired 
but  little  more  than  its  ancient  density.  Much  of  the  in- 
crease of  density  due  to  cooling  has  been  nullified  by  relief 

*  Mr.  D.  Trowbridge  expresses  the  opinion  that  "  the  angular  velocity  of  the 
external  parts  would  not  be  much  increased  except  by  friction,"  and  would  thus 
tend  to  rotate  according  to  Kepler's  third  law  (Ainer.  Jour.  Sci.,  II,  xxxviii,  357) 
Since  the  internal  parts  have  experienced  more  contraction  than  the  external,  it 
follows  that  their  rotary  velocity  must  have  been  increased  more  than  that  of  the 
external,  if  the  condensation  took  place  after  rotation  had  begun.  In  this  case, 
Mr.  Trovvbridge's  conclusion  would  be  sound.  But  it  seems  very  stipposable 
that  the  generation  of  the  rotation  was  a  later  event  than  the  aggregation  of  the 
nebulous  matter,  and  hence  the  condensation  at  the  centre  existed  before  rela- 
tion began;  and  the  development  of  that  central  density  has  not,  therefore, 
accelerated  the  central  rotation. 

t  Ennis  has  conceived  a  more  rapidly  rotating  exterior  retarded  by  friction 
upon  the  interior  as  the  explanation  of  the  apparent  discrepancy  between  theory 
and  fact  (J.  Ennis,  Origin  of  the  Stars,  chs.  xvii,  xix,  and  xxii).  But  he  supposes 
the  original  rotation  imparted  only  to  the  exterior  by  currents  descending  from 
higher  to  lower  levels  (p.  232),  and  supposes  the  interior  to  have  acquired  its 
rotation  by  friction  with  the  exterior  —  though  in  some  cases  a  general  rotation 
may  have  been  earlier  generated  by  mutual  collisions. 


166  OEIGIK   OP  THE   SOLAK   SYSTEM. 

from  the  pressure  of  abandoned  rings.  In  this  view,  the 
sun's  present  rotary  velocity  might  be  nearly  that  which 
had  been  acquired  at  a  very  early  period.  It  should,  there- 
fore, be  vastly  less  than  the  rate  required  by  the  simple 
laws  of  contraction. 

Similar  reasoning  in  reference  to  the  periods  of  Jupiter's 
satellites  shows  them  to  have  been  similarly  retarded;  but 
the  retardation  is  only  about  one-fifth  as  much  as  in  the 
case  of  the  planets.  This  is  what  we  should  expect  ac- 
cording to  the  nebular  theory,  since  the  mass  of  Jupiter  is 
much  less  than  that  of  the  sun,  and  the  difference  in  den- 
sity between  the  central  and  exterior  portions  would  be  less. 

From  these  two  general  courses  of  reasoning,  it  seems 
legitimate  to  conclude  that  the  ratios  of  the  periodic  times 
of  the  planets  resulting  from  an  annulating  nebula  which 
began  its  rotation  after  condensation  about  the  centre, 
must  approach  nearer  a  ratio  of  equality  than  they  would 
if,  as  is  generally  assumed,  the  rotation  of  the  nebula 
began  before  central  condensation  from  gravity  had  been 
effected,  and  the  velocities  of  rotation  had  been  determined 
by  the  whole  contraction.  This  diminished  ratio  of  periodic 
times  may  result  from  an  increased  relative  acceleration  of 
external  parts,  or  from  a  diminished  acceleration  of  internal 
parts  in  acting  on  the  external. 

Should  it  seem  improbable  that  rotation  began  after 
condensation  had  taken  place,  it  may  readily  be  admitted 
that  in  the  case  of  our  solar  nebula,  and  accordingly  in 
other  cases,  an  exceedingly  slow  rotation  existed  before 
full  condensation.  In  many  cases  the  initial  rotation 
would  probably  be  extremely  slow,  both  because  generally 
the  accessions  of  new  matter  would  be  relatively  so  small 
that  their  impact  would  possess  little  efficiency,  and  be- 
cause, striking,  with  equal  probability,  on  all  sides  of  the 
centre,  their  effects  would  tend  to  neutralize  each  other. 
It  will  be  borne  in  mind  also,  that  in  aggregations  as  inco- 


OBJECTIONS  FROM   PLANETARY   MOTIONS.  167 

herent    as    nebulas,    collisions    would    develop  vastly    less 
rotary  effects  than  collisions  between  solid  bodies. 

3.  The  Periodic  Times  of  the  planets  are  shorter  than 
the  Nebular  Theory  allows* — It  is  claimed  that  the  princi- 
ple of  conservation  of  areas  would  give  the  spheroid  at 
the  orbit  of  Mercury  a  period  of  rotation  equal  to  about 
eighteen  hundred  of  Mercury's  years;  so  that  Mercury 
when  detached  from  the  sun  must  have  had  about  eighteen 
hundred  times  smaller  a  quantity  of  motion  than  at  present. 
This  result  is  reached  by  taking  the  sun's  actual  rotation 
period  as  a  starting  point,  and  calculating  from  what  Mer- 
curial velocity  it  must  have  resulted  on  the  principle  of 
equal  areas. f  But  this  mode  of  calculation  is  wholly  falla- 
cious, since  we  have  abundant  reason  for  believing,  as 
already  explained,  that  the  sun's  actual  rotation  has  not 
resulted  simply  in  accordance  with  the  law  of  equal  areas 
in  a  contracting  homogeneous  medium.  Investigators  of 
this  subject  generally  admit  that  the  sun's  acceleration 
of  rotation  has  been  diminished.  Moreover,  the  great 
central  condensation  of  the  primitive  nebula  prevented 
contraction  and  acceleration  in  the  same  ratio  as  was  ex- 
perienced by  the  remoter  and  more  tenuous  zones.  The 
result  of  the  comparison  between  Mercury's  actual  veloci- 
ty and  that  which  he  must  have  had  on  the  principle  of 
equal  areas,  calculating-  back  from  the  sun,  is  precisely 
what  the  progress  of  the  nebular  evolution  would  require; 

*  Rev.  S.  Parsons,  Meth.  Quar.  Rev.,  Jan.,  1877,  p.  151. 

t  Let  R  =  radius  of  sun ;  r  =  radius  of  nebula  when  expanded  to  Mercury's 
orbit;  6'=  angular  velocity  of  the  sun,  and  0  =  angular  velocity  when  expanded 
to  Mercury's  orbit.  Then  by  the  principle  of  equal  areas, 

6:6'::R1:r*;   .'.  6  =  6'~.     Also  ^=0—-. 
But  9'=0°.59  per  hour;   #  =  4:30,000  miles;  r=  35,750,000  miles;  therefore, 

9  =  0°.00008536  per  hour.    But  Mercury's  actual  angular  velocity  is  — ^1! —  _ 

87.97  X  34 

OM705  per  hour.    Hence  his  actual  angular  velocity  is      "L^    =  1998  times  as 
rapid  as  it  should  be  on  the  principle  of  equal  areas. 


168  .  ORIGIN   OF  THE   SOLAR   SYSTEM. 

and  tends  to  confirm  the  nebular  theory  instead  of  weak- 
ening it. 

It  would  be  quite  as  legitimate  to  assume  Mercury's 
period  as  a  starting  point  and  inquire  what  must  have 
been  the  sun's  angular  velocity.  This  would  show  that 
the  sun's  velocity  is  1998  times  too  slow.  But  this  under- 
rate of  the  sun's  rotation  is  quite  in  accordance  with  our 
reasoning. 

This  objection  is  substantially  the  same  as  the  last.  In 
that  it  is  maintained  that  the  orbital  velocity  of  each 
planet  is  too  slow  in  relation  to  planets  exterior  to  it. 
Here  it  is  maintained  that  a  planet's  orbital  velocity  is 
too  rapid  in  reference  to  a  planet  interior  to  it.  The  two 
propositions  are  convertible. 

4.  The  Periodic  Time  of  Phobos,  the  inner  satellite  of 
Mars,  is  too  short.— M.  Faye,  in  the  first  of  his  important 
memoirs  on  nebular  cosmogony,*  has  presented  it  as  a 
difficulty  in  the  theory  of  Laplace  that  the  inner  satellite 
of  Mars  revolves  in  about  one-third  the  period  of  the 
planet's  rotation  on  its  axis.  "The  period  of  rotation  of  a 
planet,  said  Laplace,  must  be,  according  to  my  hypothe- 
sis, less  than  the  period  of  revolution  of  the  nearest  body 
which  circulates  around  it.  !  :  Nor  is  this  the 

sole  exception  to  the  theorem  of  Laplace.  The  same  is 
true  of  a  part  of  the  rings  of  Saturn,  as  was  observed 
some  time  since  by  M.  Roche.  There  must  exist,  therefore, 
some  defect  in  the  mother  idea  of  the  theory." 

Undoubtedly  the  Laplacean  conception  of  nebular  cos- 
mogony must  be  somewhat  modified.  Many  facts  brought 
to  light  within  the  last  three-quarters  of  a  century  are  now 

*  M.  Faye,  Comp/es  Rendus,  torn,  xc,  560,  March  15,  1880.  Prof.  C.  A.  Young 
also,  in  a  lecture  delivered  !n  New  York  in  January,  188:5,  speaking  of  the  theory  of 
Laplace,  is  reported  to  have  said,  "  Whether  this  system  can  be  true  in  its  entirety 
I  very  much  doubt.  It  is  necessary  to  suppose  some  change  in  its  mode  of  action ; 
for  otherwise  the  moons  of  Mars  never  could  revolve  quicker  than  the  rotation 
of  the  planet  itself.  Yet  something  like  this  may  be  the  correct  theory." 


OBJECTIONS    FROM    PLANETARY    MOTIONS.  169 

available  as  a  basis  for  reasoning,  and  it  is  necessary  to 
modify  some  of  the  details  of  liis  theory.  Laplace  rea- 
soned on  the  assumption  of  an  absolute  void  in  the  inter- 
planetary spaces,  and  he  obtained  only  a  first  glimpse  of 
the  influence  of  tides  upon  the  rotation-period  of  a  planet 
or  satellite.  We  now  understand  that  the  spaces  around 
us  are  thickly  occupied  by  particles  of  matter  which  I 
have  designated  "  cosmical  dust."  We  believe  generally, 
in  the  existence  of  a  material  "  ether."  The  mathematical 
theory  of  tidal  action  has  very  recently  been  followed  out 
in  its  remote  consequences  to  such  an  extent  as  to  unfold 
new  and  surprising  cosmical  effects  in  the  primitive  and 
ultimate  stages  of  planetary  life. 

I  have  already  pointed  out  the  necessary  influence  of 
the  storm  of  meteoroids  in  transforming  the  energy  of 
orbital  motion  in  any  planetary  body,  but  especially  in 
bodies  as  small  as  the  Martial  satellites.  It  is  entirely 
credible  that  the  satellites  of  Mars,  and  especially  the 
inner  and  smaller  satellite,  should  by  such  means,  have 
been  drawn  nearer  the  centre  of  their  motions,  and  thus 
accelerated  in  orbital  velocity.  When  Phobos  was  12,480 
miles  distant  from  the  centre  of  Mars,  its  period  of  revo- 
lution was  three  times  its  present  period.  It  then  very 
nearly  equalled  the  day  of  Mars,  and  was  just  fcsvo-thirds 
the  period  of  the  outer  satellite,  Deimos.* 

But  it  is  manifest  that  an  ulterior  result  of  solar  tidal 
action  upon  any  planet  whose  rotation  has  become  syn- 
chronous with  that  of  its  dominant  satellite  (whether  by 
acceleration  of  the  satellite  or  retardation  of  the  planet) 

*The  relation  between  distances  and  times  is  given  by  Kepler's  third  law 
from  which 

t:t':-.r*:  f5  and  t'=l(f  )?. 

To  find  at  what  distance  a  satellite  will  perform  its  revolution  in  a  period  n 
times  as  great,  we  have  t'=nt=t(  -)5.  From  this  r'=nsr,  and  in  the  case  of 
Phobos,  ^=31x6,000=12,480. 


170  ORIGIN   OP  THE   SOLAR   SYSTEM. 

will  be  a  further  retardation  of  the  planetary  rotation,  so 
that  the  day  will  become  longer  than  the  lunar  month,  as 
in  the  case  of  Mars  and  Phobos.  It  is  at  least  conceivable, 
on  physical  principles,  that  the  relation  of  the  motions  of 
these  two  bodies  is  an  incident  of  the  old  age  of  the 
Martial  system. 

5.  We  have  no  adequate  cause  assigned  for  the  inaug- 
uration of  a  Rotary  Motion.\ — I  believe  the  considera- 
tions heretofore  presented  (pp.  94-106)  must  convince  any 
unbiased  mind  that  the  chances  of  the  causation  of  rotary 
motion  are  nearly  as  infinity  to  unity.  It  may  be  well, 
however,  to  correct  a  misapprehension  which  has  been 
used  against  the  theorem  that  attraction  from  without 
would  inaugurate  rotation.  Mr.  Parsons  says,  in  effect, 
that  such  attraction  would,  indeed,  initiate  rotation  about 
the  shortest  axis;  but  the  prolateness  caused  would  be 
directed  constantly  toward  the  attracting  body,  and  would, 
like  a  great  tide,  promptly  arrest  the  rotation  which  had 
been  begun.  But,  as  all  nebulre  must  experience  a  mo- 
tion of  translation,  this  attracting  body  unless  moving  in 
the  line  of  the  prolate  axis,  would  finally  deflect  this  axis, 
and  as  the  body  should  pass  to  such  distance  that  the  com- 
parative influence  should  be  null,  the  prolate  nebula  would 
cease  to  be  prolate,  and  would  be  left  in  the  process  of  a 
slow  rotation.  Or  if,  while  the  attracting  body  remains 
in  the  neighborhood,  a  third  body  should  pass  through 
such  a  position  as  to  influence  one  extremity  of  the  pro- 
late axis  more  than  the  other,  this  influence  might  be 
sufficient  to  overcome  the  fixity  caused  by  the  first  attract- 
ing body.  But,  it  will  be  recalled  by  the  reader  that  the 
most  plausible  conception  of  the  forming  process  of  nebuhv 
represents  them  as  falling  together  and  acquiring  of  neces- 
sity a  rotary  motion  from  an  early  stage  of  their  existence. 

tRev.  S.  Parsons,  Methoditt.  Quarterly  Review,  January,  1877,  144-5;  Rev. 
W.  B.  Slaughter:  The  Modern  Genesis,  ch.  iii. 


OBJECTIONS   FROM    PLANETARY    POSITIONS.          171 

§  3.  OBJECTIONS  BASED  ON  RELATIONS  OF  PLANETARY 

POSITIONS. 

1.  The  inclinations  of  the  planetary  orbits  to  the  plane 
of  the  sun's  equator.* — It  is  sometimes  pretended  that  all 
the  primary  and  secondary  orbits  should  be  strictly  coinci- 
dent; and  it  is  at  once  evident  that  by  the  theory,  they  must 
have  been  so,  if  the  system  had  assumed  form  in  the 
absence  of  att  perturbctting  influences  from  without.  This 
is  the  unconditional  and  unwarranted  assumption  of  the 
objectors.  But  we  know,  in  the  first  place,  that  pertur- 
bating  influences  could  not  have  been  absent.  The  grave 
misapprehension  exists  in  some  minds  that  the  nebular 
theory  assumes  a  complete  evolution  through  the  action  of 
its  own  internal  forces  alone.  Rev.  W.  B.  Slaughter  em- 
ploys the  following  language:  "We  must  not  forget  that 
this  cosmical  sphere  is  revolving  in  a  void.  There  is  no 
external  matter  whose  friction  or  attraction  can  modify 
the  result.  If  it  be  alleged  that  there  is  other  matter  in 
the  universe  whose  attraction  must  have  reached  the  cos- 
mical sphere  and  affected  it,  we  reply  that  the  nebular 
hypothesis  does  not  take  such  external  attractions  into 
account. \  It  professes  to  find  all  its  world-forming  forces 
within  the  mass."  \  This  is  a  profound  and  fatal  miscon- 
ception, but  one  which  is  made  the  basis  of  much  of  Mr. 
Slaughter's  criticism.  In  fact  the  system  of  Neptune  is 
so  far  removed  that  we  may  say  it  feels  but  slightly  the 
controlling  influence  of  the  sun,  while  the  stellar  masses 
must  exert  an  influence  somewhat  perceptible.  A  similar 
remark  may  be  made  in  reference  to  Uranus  and  Saturn. 
Moreover  when  one  planetary  orbit  should  have  been 
thrown  out  of  coincidence  with  the  plane  of  the  solar 

*Rev.  W.  B.  Slaughter:  The  Modern  Genesis,  ch.  vi. 

tit  is  a  sufficient  reply  to  this  to  refer  the  reader  to  the  nebular  theories  of 
Kant  and  Laplace  presented  in  part  IV,  chap,  ii  and  iv. 
J  The  Modern  Genesis,  68,  69. 


172  ORIGIN    OF   THE   SOLAR   SYSTEM. 

equator,  it  would  act  on  all  the  other  planets  to  produce 
the  same  kind  of  disturbance.  That  the  inclinations  in 
question  are  affected  by  the  mutual  attractions  of  the 
planets  is  a  well  settled  principle  in  cosmical  physics;  and 
nothing  is  more  supposable  than  that  the  whole  value  of 
the  inclinations  has  been  created  by  these  or  kindred 
causes.  Sir  Isaac  Newton  says:  "  While  comets  move  in 
very  eccentric  orbits  in  all  manner  of  positions,  blind  fate 
could  never  make  all  the  planets  move  in  one  and  the 
same  way  in  orbits  concentric,  some  irregularities  excepted 
which  may  have  risen  from  the  mutual  actions  of  comets 
and  planets  upon  each  other,  and  which  will  be  apt  to 
increase  till  this  system  wants  a  reformation."  *  How- 
ever, in  spite  of  Newton's  apprehension,  we  now  know, 
from  the  progress  of  the  recognized  oscillations  in  these 
planes,f  it  is  ascertainable  that  in  the  course  of  time  they 
return  nearly  to  the  positions  from  which  theory  supposes 
them  to  have  started.  Thus  it  appears  that  Mercury  will 
sometimes  coincide  with  the  plane  of  the  sun's  equator; 
Venus  will  approach  within  5°  25';  the  earth  within  3°; 
Mars,  within  10°;  Jupiter,  within  5°;  Saturn,  within  5°  5'; 
Uranus,  within  5°,  and  Neptune  within  5°  8'.  Similarly, 
the  plane  of  the  moon's  orbit  will  approach  to  within  18° 
of  coincidence  with  the  plane  of  the  earth's  orbit.  The 
proper  plane  of  reference,  however,  for  these  inclinations 
is  not  the  ecliptic,  which  is  only  the  position  in  which  the 
ever-changing  plane  of  the  earth's  orbit  happens  to  lie  at 
the  present  time,  but  the  "  invariable  plane  of  the  solar 
system."  With  this  the  planets  make  only  the  angles 
indicated  thus:  Mercury,  6°  20'  58";  Venus,  2°  11'  14"; 
Earth,  1°  35'  19";  Mars,  1°  40'  44";  Jupiter,  0°  20'; 
Saturn,  0°  55'  31";  Uranus,  1°  1'  45";  Neptune,  Oc  43' 
25".  In  the  course  of  time  these  inclinations  will  reach 

*  Newton :  Optics,  p.  376. 

t  See  Stockwell,  Smithsonian  Contributions  to  Knowledge,  xviii. 


OBJECTIONS   FKOM   PLANETARY   POSITIONS.          173 

the  following  minima:  Mercury,  4°  44'  27";  Venus,  0°  0' 
0";  Earth,  0°  0'  0";  Mars,  0°  0'  0";  Jupiter,  0°  20';  Sat- 
urn, 0°  47'  16";  Uranus,  0°  54'  25";  Neptune,  0°  33' 
43".*  Now  it  would  seem  that  instead  of  any  material 
conflict  with  the  theory  in  this  state  of  facts,  we  discover 
an  impressive  confirmation  of  it. 

2.  The  Breadth  of  Intervals  between  the  planetary 
orbits  is  not  clearly  explained  on  the  nebular  theory.^ — It 
has  been  suggested  that  instead  of  a  periodic  disengage- 
ment of  a  ring  of  considerable  mass,  the  equatorial  peri- 
phery would  continuously  flatten  out  into  a  continuous 
disc-like   expansion;    so  that  nearly  the  whole  nebulous 
mass  would  ultimately  assume  a  discoid  or  flatly  lenticular 
form,  when  annulation  and  planetation  would  take  place 
in  all  the  rings  simultaneously.    Under  this  view  the  rings 
should  be  more  numerous,  or  at  least  more  approximated 
to  each  other.     I   have  given  this  subject  considerable 
study,  and  have  reached  the  conclusion  that  the  original 
opinion  of    Laplace  is  the  more  probable  one.      I   have 
attempted  to  show  |  that  the  act  of  annulation  would  be 
periodic,  and   the  reader  is   referred   to  the   statements 
already  made.§     The  intervals  between  the  planetary  orb- 
its,   therefore,    instead    of    conflicting   with   the    nebular 
theory,  ought  to  be  cited  as  confirmation. 

It  might  be  said  further,  that  the  various  inclina- 
tions of  the  planes  of  the  planetary  orbits  is  a  circum- 
stance less  likely  to  result  from  a  simultaneous  origin  of 
the  planets  than  from  successive  origins. 

3.  The  nebular  theory  does  not  account  for  the  Elliptic 
Forms  of  the  planetary  Orbits. — The  equatorial  periphery 

*,J.  N.  Stockwell,  Smithsonian  Contributions,  xviii,  Doc.  232,  pp.  166,  169. 

t  Ncwcomb:  Popular  Astronomy,  497-8.  This  is  not  presented  by  Professor 
Newcomb  as  a  fatal  difficulty,  but  is  only  alleged  against  a  non-esseiitial  feature 
of  the  Laplacean  hyi>othesis. 

$  Part  I,  Chap,  ii,  §  3,  3. 

§  Hinrichs  concludes  that  the  process  of  annulation  would  be  periodic,  and 
that  the  intervals  would  be  equal  (Amer.  Jour.  Sci.,  II,  xxxix,  140  1, 144-7). 


174  ORIGIN    OF   THE   SOLAR   SYSTEM. 

of  the  rotating  nebula  must  have  been  at  all  times  nearly 
circular.  This  would  result  in  a  circular  ring  and  a  circu- 
lar orbit  for  the  planet.  Let  us  examine  the  point. 

(1.)  I  have  stated  above  (p.  160)  that  a  reduction  of  the 
central  mass  S,  Figure  35,  would  cause  the  planet  to 
retreat.  It  is  scarcely  supposable  that  a  motion  away 
from  S  would  be  inaugurated  without  carrying  the  planetj 
by  virtue  of  its  inertia,  beyond  the  point  of  equilibrium 
between  centrifugal  and  centripetal  forces.  Brought  to  a 
halt  at  a  point  beyond  this  equilibrium,  it  would  be  in  the 
position  of  a  body  let  fall  toward  S,  but  actuated  at  the 
same  time  by  a  strong  transverse  impulse.  I  have  already 
explained  (p.  67)  that  under  such  circumstances  the  planet 
would  describe  an  elliptic  path  around  the  centre  of 
attraction. 

It  is  not  necessary  to  conceive  the  planet  as  retreating 
with  the  suddenness  indicated  by  the  dotted  line  Ac.  The 
result  would  be  the  same  whatever  number  of  revolutions 
it  might  make  in  reaching  its  remotest  point. 

If  these  views  are  correct,  the  amount  of  a  planet's 
eccentricity,  other  things  being  equal,  should  be  propor- 
tional to  the  mass  of  the  planet  next  interior.  Saturn, 
with  the  planet  Jupiter  next  interior,  should  have  a 
greater  eccentricity  than  Uranus  with  the  mass  of  Saturn 
next  interior.  Accordingly  the  eccentricity  of  Saturn  is 
.056,  while  that  of  Uranus  is  .046.  So  the  eccentricity  of 
Mars  should  be  greater  than  that  of  the  earth.  In  fact 
the  eccentricity  of  Mars  is  .093,  while  that  of  the  earth  is 
.017.  So  the  eccentricity  of  the  earth, .017,  as  determined 
by  the  withdrawal  of  Venus,  is  greater  than  that  of 
Venus,  .007,  as  determined  by  the  withdrawal  of  the 
smaller  planet  Mercury.  The  eccentricity  of  Mercury  is 
.206  with  no  interior  planet  certainly  known  to  have 
caused  it.  Until  a  considerable  interior  mass  is  demon- 
strated, it  is  allowable  to  attribute  this  comparatively 


OBJECTIONS   FROM    PLANETARY    MASSES,  ETC.        175 

large  eccentricity  to  the  proximity  of  Mercury  to  the 
perihelia  of  cometary  and  other  erratic  bodies  drawn 
toward  the  sun.  Most  of  the  asteroids  have  large  eccen- 
tricities; but  these  may  be  attributed  chiefly  to  the  influ- 
ence of  neighboring  planets,  especially  of  Jupiter.  The 
small  masses  of  Mercury  and  the  asteroids  would,  of 
course,  render  them  specially  susceptible  to  perturbative 
influences. 

(2.)  The  circular  orbit  is  one  of  unstable  equilibrium 
in  the  actual  universe.  It  is  impossible  of  conservation. 
Every  external  attraction  to  which  the  planet  might  be 
subjected  would  pull  it  from  its  path. 

Suppose  a  planet  revolving  in  a  circular  orbit,  the  per- 
turbative influence  of  any  attractive  body,  as,  for  instance, 
a  neighboring  planet,  would  draw  it  from  a  circular  path; 
and  as  that  influence  should  again  diminish,  the  planet 
would  swing  toward  its  circular  orbit  again.  But  it  would 
swing  too  far.  By  the  laws  of  mechanics  we  know  that  its 
orbit  would  henceforth  be  elliptic.  It  is  shown  as  the 
result  of  the  most  elaborate  calculations,  that  the  eccen- 
tricity of  each  planetary  orbit  is  actually  affected  by  the 
attraction  of  each  sister  planet;  and  the  value  of  the 
eccentricity  increases  and  diminishes  according  as  the 
resultant  perturbation  increases  or  diminishes  in  amount. 
Beyond  all  question  this  cause  must  convert  an  original 
circular  orbit  into  an  elliptic  one. 

§  4.   OBJECTIONS  BASED  ON  RELATIONS  OF  PLANETARY 
MASSES  AND  DENSITIES. 

1 .  The  mass  of  the  Asteroids  is  smaller  than  the  nebular 
theory  requires. — All  the  asteroids  known  aggregate  less 
than  YoVtf  tne  Du^  °f  tne  earth,  and  their  mass  probably 
is  much  less  in  proportion.  Leverrier  calculated  that  the 
greatest  possible  mass  of  all  the  asteroids,  discovered  and 
undiscovered,  could  not  exceed  one-fourth  of  the  earth's 


176  ORIGIN    OF   THE   SOLAR   SYSTEM. 

mass.  Such  an  asteroidal  mass  would  explain  the  secular 
motion  of  the  perihelion  of  Mars.  But  a  revised  determina- 
tion of  the  earth's  mass  shows  that  the  earth's  influence  is 
almost  sufficient  to  account  for  this  secular  motion;  and 
hence  the  total  asteroidal  mass  must  be  exceedingly  small. 
But  I  am  not  aware  that  the  nebular  theory  necessitates 
any  direct  simple  relation  between  the  masses  of  the 
planets  in  a  system,  though  it  is  true  that  the  mass  of  each 
planet  is  connected  with  its  period  of  revolution  and  mean 
distance  from  the  body  around  which  it  revolves.  It  is 
also  true  that  in  general  we  should  expect  the  remoter 
planets  to  possess  larger  masses  because  formed  from  rings 
having  larger  circumferences.  This  is  generally  the  case, 
and  is  so  far  a  confirmatory  circumstance.  But  the  theory 
carried  out  in  the  midst  of  space  already  populated  by 
numberless  moving  bodies  does  not  forbid  the  disengage- 
ment of  rings  of  small  mass.  The  asteroidal  and  the 
Martial  masses  may  both  have  been  originally  less  than 
the  principle  of  regular  gradation  permits.  But  it  may 
also  be  suggested  that  both  these  masses  may  have  been 
reduced  from  their  original  amounts  by  precipitation  of 
portions  into  the  solar  nebula  before  the  latter  had 
shrunken  sufficiently  within  the  perihelion  positions  of 
these  masses.* 

2.  The  Disrupted  State  of  the  asteroidal  mass  is  an 
Anomaly  in  the  operation  of  the  theory. — The  circumstance 
is  extraordinary,  but  not  anomalous.  The  Saturn ian  rings 
are  extraordinary,  but  so  far  from  anomalous  that  they 
bring  strong  testimony  to  the  soundness  of  the  theory. 

(1.)  I  have  heretofore  (p.  119)  suggested  the  probability 
of  the  stratification  of  the  nebulous  rings.  This  suggestion 
seems  to  have  occurred  to  Laplace.  Now,  with  the  dis- 
ruption of  a  stratified  ring,  it  is  quite  conceivable  that 
numerous  planets  might  result,  while  it  is  equally  con- 

*  As  suggested  by  D.  Kirkwood,  Amer.  Jour.  Sd.,  Ill,  i,  71. 


OBJECTIONS   FROM    PLANETARY    MASSES,  ETC.        177 

ceivable  that  they  might  coalesce  into  one.  Either  con- 
tingency is  entirely  within  the  provisions  of  the  theory. 

(2.)  Moreover,  it  was  a  suggestion  of  the  late  Professor 
Benjamin  Peirce  that  an  intra-Jovian  ring  might  have 
persisted  until  excess  of  perturbation  and  consequent 
oscillation  "brought  it  into  contact  with  the  planet  Mars, 
by  which  collision  it  was  broken  into  asteroids.* 

(3.)  Finally,  Professor  Clerk-Maxwell  in  investigating 
the  conditions  of  equilibrium  of  Saturn's  rings,  f  reached 
the  conclusion  that  undulations  in  a  fluid  ring,  under 
certain  circumstances,  would  result  in  breaking  up  the 
ring  into  small  satellites.  Mr.  Trowbridge  has  applied 
this  conclusion  to  a  ring  persisting  between  Mars  and 
Jupiter  until  it  had  attained  the  condition  of  an  incom- 
pressible fluid,  when  it  would,  at  a  later  period,  be  broken 
into  a  multitude  of  asteroids. 

The  possibilities  of  the  nebular  theory  therefore  deprive 
of  all  force  any  objection  based  on  the  existence  of  a 
group  of  asteroids.^ 

3.  The  densities  of  the  outer  planets  are  so  low  that  if 
composed  of  the  same  materials  as  the  earth  they  should 
be  of  a  temperature  sufficiently  high  to  be  self-luminous.% 
— All  recent  observations  lead  Coward  the  opinion  that  these 
planets  are  enveloped  in  a  thick  mantle  of  aqueous  vapors. 
It  is  only  the  exterior  of  this  envelope  which  is  exposed 
to  our  view.  On  planets  of  such  mass,  the  density  and 

*  B.  Peirce,  Gould's  Astronomical  Journal,  ii,  18;  also  Annual  of  Scientific 
Discovery,  1852,  379.  Compare  G.  Hinrichs,  Amer.  Jour.  Sci.,  II,  xxxix,  54. 

t  Clerk-Maxwell :  On  the  Stability  of  the  Motions  of  Saturn's  Kings,  1856. 

J  Mr.  Herbert  Spencer  adheres  to  Giber's  theory  of  an  exploded  planet,  and 
sets  forth .the  grotesque  conception  of  a  planet  liquefying  and  even  solidifying 
around  a  gaseous  nucleus,  the  tension  of  which  finally  overcomes  the  strength 
of  the  shell  (Spencer,  Westminster  Review,  Ixx,  123,  July,  1858;  Essays,  Scientific, 
Political  and  Speculative,  second  series,  New  York,  1864).  Other  suggestions  in 
this  essay  must  be  regarded  as  entirely  an  evolution  from  inner  consciousness, 
among  which  that  of  hoop-shaped  rings  is  sufficiently  extraordinary  and  gratui- 
tous. 

§  Kev.  W.  B.  Slaughter:  The  Modern  Genesis,  ch.  xiii. 
12 


178  ORIGIX    OF   THE    SOLAR   SYSTEM. 

perhaps  the  vapor-bearing  height  of  the  atmosphere  must 
be  many  times  greater  than  on  the  earth.  By  all  this 
amount  then,  the  diameter  of  the  aqueous  envelope  ex- 
ceeds that  of  the  planetary  body.  Our  exaggerated  esti- 
mate of  the  diameter  of  the  planet  results  in  an  underesti- 
mate of  its  density.  After  making  alt  corrections,  and 
admitting  that  Jupiter  is  still  in  a  heated  condition,  it  does 
not  appear  that  the  densities  of  the  outer  planets  are  at 
all  different  from  what  the  nebular  theory  requires;  since 
that  demands  progressive  increase  in  density  toward  the 
centre.  (But  see  Chap,  iii,  §§  5  and  6,  and  Chap,  iv,  §  5.) 

A  fundamental  fallacy,  which  develops  itself  in  many 
other  forms,  is  the  assumption  that  the  nebulous  spheroid 
proceeded  to  increase  in  density  precisely  in  proportion  to 
its  diminution  in  volume,  and  that  the  rate  of  contraction 
must  be  exactly  in  the  inverse  ratio  of  the  mass.  The 
contraction  is  proportioned  to  the  loss  of  heat  in  the 
whole  mass.  The  power  of  radiation  is  proportioned  to 
the  surface;  and  the  loss  of  heat  is  in  the  same  proportion, 
provided  the  temperature  of  the  whole  mass  diminishes 
equally.  But  the  surface  is  proportional  to  the  square  of 
the  radius,  while  the  mass,  when  the  density  is  uniform, 
is  proportional  to  the  cube  of  the  radius.  In  other  words, 
the  surface  diminishes  more  slowly  than  the  mass;  so  that 
the  rate  of  radiation  diminishes  less  rapidly  than  the  mass 
even  when  the  whole  mass  cools  uniformly.  But  no 
large  mass  can  cool  with  complete  uniformity;  and  in  a 
mass  which  has  become  solid  on  the  exterior  or  through- 
out, so  as  to  prevent  convection  of  heat  by  free  mobility 
of  the  particles,  the  rate  of  cooling  will  be  also  retarded 
by  the  process  of  conduction  from  the  interior  to  the  sur- 
face. Hence  every  planetary  mass  must  proceed  at  a  con- 
tinually retarded  rate  of  cooling. 

For  these  reasons  no  two  planets  of  the  same  mass  can 
have  attained  to  temperatures  proportioned  to  their  ages. 


OBJECTION    FROM    TERRESTRIAL    DURATION.          179 

The  temperature  is  a  function  of  the  age,  but  not  a  simple 
function  of  it.  Nor  can  two  planets  of  the  same  age  but 
of  different  masses  have  attained  to  thermal  conditions 
proportional  to  the  masses.  Nor,  if  the  thermal  condi- 
tions were  the  same,  would  their  densities  be  the  same. 
Density  depends  on  thermal  conditions  and  on  mass. 
Hence  all  the  captious  criticisms  on  the  nebular  theory 
based  on  supposed  non-conformities  of  the  planetary  densi- 
ties are  founded  on  misapprehension  of  the  physical  con- 
ditions involved. 

§  5.    OBJECTION  BASED  ON  RELATION  TO  TERRESTRIAL 
DURATION. 

The  nebular  theory  does  not  admit  as  great  an  Age  for 
the  World  as  geology  requires.* — Sir  William  Thomson,  on 
the  basis  of  the  observed  principles  of  cooling,  concludes 
that  not  more  than  ten  million  years  can  have  elapsed 
-since  the  temperature  of  the  earth  was  sufficiently  reduced 
to  sustain  vegetable  life;f  and  on  the  duration  of  tidal 
action  reaches  a  similar  result.  J  Helmholtz  calculates  that 
twenty  million  years  would  suffice  for  the  original  nebula 
to  condense  to  the  present  dimensions  of  the  sun.  Pro- 
fessor S.  Newcomb  requires  only  ten  million  years  to 
attain  a  temperature  of  212°  Fahr.§  Croll  estimates  seventy 
million  years  ||  for  the  diffusion  of  the  heat  which  would 
be  produced  by  the  collision  of  two  such  nebulas  as  would 
constitute  the  primitive  nebula  postulated  by  the  theory. 
But  meantime  Bischof  calculates  that  350  million  years 
would  be  required  for  the  earth  to  cool  from  a  temperature 

*  Rev.  S.  Parsons,  Meth.  Quar.  Rev.,  Jan.,  1877,  pp.  142-3. 

t  Thomson  and  Tait:  Natural  Philosophy,  Appendix  D,  also  §§  832.  833,  834, 
847,  848  (but  847-9  cancelled  in  Glasgow  address) ;  Trans.  Roy.  Soc.  Edinb.,  xxiii, 
pt.  I,  157, 1863. 

J  Thomson.  Trans.  Geol.  Soc.,  Glasgow,  iii,  1. 

§Xewcomb:  Popular  Astronomy,  509. 

I  Croll:  Climate  and  Time,  335. 


180  ORIGIN    OF   THE   SOLAR   SYSTEM. 

of  2,000°  to  200°  centigrade.  Reade,  basing  his  estimate 
on  observed  rates  of  denudation,  demands  500  million 
years  since  sedimentation  began  in  Europe.*  Lyell  ven- 
tured a  rough  guess  of  240  million  years;  Darwin  thought 
300  million  years  demanded  by  the  organic  transformations 
which  his  theory  contemplates;  and  Huxley  is  disposed  to 
demand  a  thousand  millions.  "Here,"  savs  Mr.  Parsons, 
"is  a  clear  conflict  between  the  naturalist  and  philosopher. 
Either  the  geologist  must  be  compelled  to  surrender  some 
hundreds  of  millions  of  time,  or  the  physicist  must  give 
up  the  nebular  theory  as  the  foundation  of  the  condensa- 
tion hypothesis  of  the  sun's  heat  and  the  earth's  present 
temperature.  The  geologist  will  probably  carry  the  day, 
and  the  nebular  hypothesis  will  have  to  give  way  to  some 
other  speculation  relative  to  the  origin  of  the  solar  system." 
A  better  considered  view  of  this  diversity  of  estimates 
seems  to  me  to  be  the  following:  Some  biologists,  im- 
pressed by  the  slowness  of  organic  transformations,  seem 
to  close  their  eyes  tight  and  leap  at  one  bound  into  the 
abyss  of  millions  of  years,  of  which  they  have  no  more 
adequate  estimate  than  of  infinity.  They  have  a  sort  of 
impression  that  some  hundreds  of  millions  would  not  be 
too  much.  They  are  destitute  of  the  first  exact  chrono- 
logical datum  from  which  to  set  out.  Similarly,  certain 
physical  geologists  having  roughly  estimated  the  rate  at 
which  erosion  is  going  on,  make  this  best  attainable 
knowledge  the  basis  of  a  provisional  calculation  of  the 
time  required  for  all  the  erosion  which  they  suppose  to 
have  taken  place.  Manifestly,  the  result  involves  too 
many  guesses  and  estimates  and  best  judgments  to  be  of 
any  value  in  subverting  the  significance  of  the  uniformities 
of  the  solar  system  and  the  starry  heavens.  Lastly,  the 
physicists  have  proceeded  from  more  exact  data,  and  by 
more  exact  methods,  to  results  embracing  fewer  unascer- 

*Readc,  Address  Liverpool  Geol.  Soc.,  1876. 


OBJECTIONS   PROM    COMETS,  STARS   AND   NEBULAE.  181 

tained  elements  and  fewer  assumptions  than  in  either  of 
the  other  cases.  The  shorter  periods  are,  therefore,  far 
most  likely  to  represent  the  truth;  and  these  are  derived 
according  to  the  principles  of  the  nebular  theory. 

I  shall  hereafter  show  that  physical  science  places  the 
geologist  in  possession  of  facts  which  enable  him,  without 
receding  from  his  best  methods  of  calculation,  to  deduce 
a  value  for  the  age  of  the  world,  which  lies  quite  within 
the  limits  fixed  by  physical  investigation.  The  great  fact 
to  which  I  allude  is  the  enormous  exaggeration  of  the 
forces  of  sedimentation  in  the  world's  early  history,  due  to 
the  enormous  development  of  tidal  action  at  a  time  when 
the  lunar  mass  was  much  nearer  the  earth  than  at  present. 

The  conflict,  therefore,  between  the  physicists  and  the 
geologists  is  entirely  imaginary.  Even  if  it  were  real,  it 
would  be  no  more  than  a  conflict  between  vague  opinion 
and  the  results  of  calculations  which  themselves  embody 
many  data  which  are  merely  assumed. 

§  6.    OBJECTIONS   BASED   ON    RELATIONS   OP   COMETS, 
STARS  AND  NEBULAE. 

1.  Cometary  phenomena  ought  to  be  provided  for 
under  the  nebular  theory,  but  this  is  impossible* — This 

*Rey.  S.  Parsons,  Methodist  Quarterly  Review,  January,  1877,  pp.  132-4. 
Compare  the  views  of  D.  Kirkwood,  American  Journal  of  Science,  II,  xxxviii, 
16-18,  who  thinks  a  majority  of  the  periodic  comets  have  originated  in  the  sys- 
tem, and  says  Faye's  comet  "  may  be  regarded  as  a  connecting  link  between 
planets  and  comets."  Mr.  Herbert  Spencer,  also,  has  undertaken  to  show  that 
many  more  comets  approach  our  sun  from  the  direction  of  the  poles  of  the  ecliptic 
than  from  the  direction  of  its  plane;  and  hence  indicate  a  physical  connection 
with  our  system  ( Westminster  Review,  Ixx,  110-12,  July,  1858).  He  thinks  comets 
to  be  mere  detached  flocculi  left  behind  during  the  contraction  of  the  solar  nebula. 
Much  information  in  reference  to  comets  and  their  connection  with  meteoric 
matter  has  been  gained  since  Mr.  Spencer  wrote,  and  his  suggestion  does  not 
seem  as  plausible  as  it  did.  Moreover,  if  comets  have  chiefly  originated  within 
the  sphere  of  attraction  of  our  system,  it  is  improbable  that  so  many  of  them 
should  have  acquired  hyperbolic  orbits  which  carry  them  indefinitely  beyond 
the  controlling  influence  of  our  sun.  Nor  does  it  seeni  credible  that  after  time 
enough  has  elapsed  to  form  and  consolidate  so  many  planets,  those  cometary 


182  ORIGIN    OF   THE   SOLAR   SYSTEM. 

pretence  is  totally  inadmissible.  Only  two  reasons  have 
been  presented  on  which  it  can  be  based:  (1.)  Some  of 
the  comets  have  eccentricities  but  little  greater  than  those 
of  a  few  of  the  asteroids,  and  thus  a  gradation  exists  from 
the  planetary  orbit  nearly  circular  to  the  cometary  orbit 
with  extreme  eccentricity.  (2.)  That  a  physical  connec- 
tion actually  exists  between  the  comets  and  planets  is 
shown  by  the  coincidences  between  the  aphelia  of  groups 
of  comets  and  the  mean  distances  of  certain  planets,  espe- 
cially the  four  outer  ones. 

Now,  the  objections  to  this  claim,  in  addition  to  the 
suggestions  thrown  into  a  note,  are  the  following: 

(1.)  Neither  Laplace  nor  any  subsequent  astronomer  has 
been  impressed  by  any  such  relations  between  the  comets 
and  planets  as  to  suggest  that  they  belong  to  the  same  sys- 
tem, or  have  had  a  common  history.  Laplace  says:  "  In  our 
hypothesis  the  comets  are  strangers  to  the  planetary  sys- 
tem. In  regarding  them,  as  we  have  done,  as  small  nebu- 
lae wandering  from  solar  system  to  solar  system,  and 
formed  by  the  condensation  of  nebulous  matter  spread 
with  such  profusion  through  the  universe,  it  is  apparent 
that  when  they  arrive  in  that  part  of  space  where  the 
attraction  of  the  sun  is  predominant,  he  forces  them  to 
describe  elliptic  or  hyperbolic  orbits.  But  their  movements 

flocculi  should  be  just  arriving;  nor,  if  just  arriving,  should  they  be  seen  mov- 
ing with  velocities  which  would  carry  them  across  the  diameter  of  our  system  in 
a  few  years  and  across  the  sphere  of  our  sun's  attraction  in  a  few  centuries.  As 
to  Mr.  Spencer's  first  assumption,  the  facts  of  the  case  have  been  collated  by 
Lamont,  and  stand  as  follows:  Of  comets  having  an  inclination  to  the  ecliptic 
ranging  from  0°  to  30°,  24  have  direct  motion  and  15  retrograde.  Of  those  from 
30°  to  60°,  34  have  direct  motion  and  42  retrograde.  Of  those  from  00°  to  90°, 
27  have  direct  and  29  retrograde  motion.  Thus,  their  inclinations  are  somewhat 
equally  distributed  from  the  equator  to  the  pole.  At  the  same  time,  we  notice 
the  concurrent  fact  that  eighty-five  of  these  comets  have  direct  motion  and  86 
retrograde.— Lament:  Astronomie  und  Erdmagnelismus,  Stuttgart,  41. 

M.  Faye  also  records  the  opinion  that  the  comets  belong  to  our  system,  and 
in  the  modified  nebular  theory  which  he  has  advanced,  attempts  to  show  how 
their  eccentric  movements  might  have  originated  (CompUs  fiendus,  tome  xc, 
pp.  640-2). 


OBJECTIONS    FROM    COMETS,  STARS   AND    NEBULAE.  183 

being  equally  possible  in  all  directions,  they  should  move 
indifferently  in  all  directions,  and  with  all  inclinations  to 
the  ecliptic,  a  demand  which  conforms  to  what  we  observe. 
Thus  the  condensation  of  nebulous  matter  by  which  we 
proceed  to  explain  the  movements  of  rotation  and  revolu- 
tion of  the  planets  and  satellites  in  the  same  direction, 
and  in  nearly  the  same  plane,  explains  equally  why  the 
movements  of  the  comets  depart  from  this  general  law."  * 

(2.)  It  signifies  nothing  if,  out  of  hundreds  of  comets 
which  have  been  recorded,  we  are  able  to  select  a  few 
with  small  eccentricity.  The  very  theory  which  we  main- 
tain in  reference  to  the  origin  of  the  comets  requires  that 
some  of  them  should  have  direct  motion  and  a  minimum 
of  cometary  eccentricity.  But  it  also  implies  that  among 
the  whole  number  of  comets,  retrograde  motion  should  be 
nearly  as  common  as  direct  motion,  arid  that  many  of  the 
cometary  orbits  should  be  ellipses  of  extreme  eccentricity, 
or  even  parabolic  or  hyperbolic  —  all  according  to  actual 
observation.  The  objector  is  not  at  liberty  to  employ  cer- 
tain exceptional  characteristics  of  a  group  of  phenomena 
in  determining  upon  a  classification;  he  is  bound  to  take 
account  of  the  entire  assemblage  of  characters.  This 
principle  of  reasoning  is  so  elementary  that  one  can  hardly 
account  for  its  disregard  except  through  a  spirit  of  cap- 
tious criticism. 

(3.)  A  physical  connection  certainly  exists  between  the 
comets  and  the  planets,  and  the  two  classes  could  not  co- 
exist in  the  presence  of  each  other  without  manifesting  it; 
but  this  does  not  imply  that  such  interaction  has  always 
existed,  or  that  the  two  classes  of  bodies  have  had  a  com- 
mon history.  Introduce  any  other  strange  body  into 
the  system,  and  the  same  kind  of  physical  connection 
would  be  immediately  established.  It  is  generally  under- 
stood that  a  cometary  body  entering  the  system  is  very 

Laplace :  Systeme  du  Monde,  ed.  1824,  p.  414. 


184  ORIGIN    OF   THE   SOLAR   SYSTEM. 

likely  to  be  so  attracted  by  some  one  of  the  planets  that  a 
new  career  and  a  new  pathway  must  date  from  the  time 
and  place  of  such  disturbance.  A  comet  starting  on  a 
new  career  from  the  orbit  of  Jupiter  might  thenceforward 
move  in  an  elliptic  orbit  having  its  aphelion  at  about  the 
distance  of  Jupiter  from  the  sun. 

2.  The  requisite  Tenuity  of  the  assumed  nebula  infill- 
ing the  orbit  of  Neptune  would  result'  in  its  Dissipation 
into  infinite  space.* — Since,  under  standard  conditions  of 
pressure  and  temperature  at  the  earth's  surface,  the  mole- 
cules of  hydrogen  have  a  motion  among  themselves  of  an 
average  velocity  of  6,000  feet  per  second,  and  those  of 
oxygen  1,800  feet,  and  those  of  air  1,400  feet  per  second, 
these  velocities  would  be  so  increased  in  the  supposed 
nebula  that  the  molecules  would  fly  off  into  space.  It  is 
calculated  that  at  a  freezing  temperature  the  motion  of 
hydrogen  atoms  would  be  9,000  feet  per  second,  while  a 
velocity  of  520  feet  per  second  would  be  sufficient  to 
overcome  the  restraining  force  of  gravity.  Still  more 
would  this  be  the  case  if  the  nebula  were  intensely  heated. 

I  do  not  conceive  it  necessary  to  discuss  the  merits  of 
a  speculation,  one  of  the  consequences  of  which  is  to 
negate  the  existence  of  something  which  stands  revealed 
to  the  ocular  sense.  The  speculation  concludes  that  a 
nebula  sufficiently  tenuous  could  not  exist,  and  here  it  is 
existing  before  our  eyes.  What  are  those  faint  films 
described  by  Sir  William  Herschel  as  barely  discernible 
in  his  great  telescope  and  spreading  over  several  square 
degrees  of  space  ?  f  What  is  the  nature  of  the  zodiacal 
light?  What  is  the  tenuity  of  the  tails  or  even  the 
comae  of  comets,  through  thousands  of  miles  of  which 
faint  starlight  is  able  to  pierce,  and  which  are  so  unsub- 
stantial that  the  entire  cometary  collection — nucleus,  coma 

*Rev.  S.  Parsons,  Meth.  Quar.  Rev.,  Jan..  1877,  pp.  141-2. 

t  Herscbel,  On  nebulous  stars,  properly  so-called,  Phil.  Trans.,  1791. 


OBJECTIOHS   FROM   COMETS,  STARS   AND   NEBULAE.  185 

and  tail — is  unable  to  disturb  perceptibly  the  movements 
of  bodies  as  small  as  Jupiter's  satellites?  If  these  are 
not  examples  of  matter  sufficiently  tenuous,  which,  not- 
withstanding their  tenuity,  are  held  together  by  the 
attraction  of  their  parts,  we  should  inquire  what  adequate 
warrant  exists  for  the  assumption  that  material  molecules 
possess  the  power  of  continuous  motion  in  one  direction 
rather  than  a  vibrating  motion.  And  whether  their  mo- 
tion is  not  instituted  and  limited  by  the  immediate  neigh- 
borhood of  other  molecules.  And  whether  it  is  not 
conceivable  that  molecular  attraction  would  restrain  neigh- 
boring molecules  from  flying  off  an  indefinite  distance. 
And  whether,  finally,  the  objector  has  ascertained  what 
degree  of  tenuity  would  so  separate  molecules  or  atoms 
that  each  in  its  motion  should  fail  to  strike  another  atom 
or  molecule  and  be  turned  back  by  it. 

But  another  point  is  overlooked  by  the  objector.  When 
it  is  calculated  that  the  matter  of  the  solar  system  uni- 
formly distributed  through  a  sphere  having  a  diameter 
equal  to  Neptune's  orbit,  would  possess  a  certain  extreme 
degree  of  tenuity,  this  is  merely  a  calculation.  It  may 
serve  to  give  us  a  conception  of  the  vastness  of  the  space, 
but  does  not  teach  us  anything  respecting  the  actual 
tenuity  or  condition  of  nebulous  matter.  The  tail  of  a 
comet  is  not  a  continuous  gas.  The  matter  of  the  zodi- 
acal light  is  composed  of  discrete,  solid  particles.  The 
nebulous  rings  of  Saturn  are  not  a  continuous  gas.  Our 
conception  of  the  crude  condition  of  nebular  matter  views 
it  as  a  cloud  of  floating  masses  and  particles  more  or  less 
dissociated,  but  tending  slowly  toward  aggregation.  Tens 
and  hundreds  of  miles  may  intervene  in  some  places. 
Each  has  its  own  motion  in  addition  to  the  general  mo- 
tion of  the  cloud;  and  hence  collisions  frequently  occur. 
If  any  aeriform  matters  exist,  or  are  brought  into  exist- 
ence, they  are  gathered  chiefly  about  the  masses  and 


186  ORIGIN   OP  THE   SOLAR  SYSTEM. 

particles.  In  a  more  advanced  stage  the  collisions  have 
become  sharper,  and  the  products  and  effects  of  collisions 
more  conspicuous.  Permanent  luminosity  begins  to  be 
maintained  in  the  interior  of  the  cloud,  and  gaseous  media 
become  more  abundant.  But  I  do  not  conceive  the 
necessity  of  assuming  that  all  the  intervening  spaces  are 
filled  with  any  form  of  matter;  since  the  attractions  of  the 
solid  or  liquid  parts  might  limit  the  action  of  an  expan- 
sive tendency,  as  has  been  generally  conceived  in  refer- 
ence to  the  atmospheres  of  the  planets.  Meantime  the 
heavier  parts  gradually  settle  nearer  the  centre  of  the 
nebulous  cloud.  Other  nebulous  clouds  are  precipitated 
upon  this.  Higher  temperature,  more  general  luminosity 
and  more  active  rotation  result.  While  the  progress  of 
aggregation  continues,  the  evolution  of  a  planetary  system 
begins.  Even  at  this  stage  we  are  not  bound  to  assume 
that  absolute  continuity  of  substance  extends  through  the 
nebula.  (But  see  Part  I,  ch.  i,  §  7.) 

3.  It  is  not  physically  probable  that  a  ring  would 
ever  be  detached.* — As  acceleration  should  increase  the 
equatorial  protuberance,  the  transfer  of  particles  from 
higher  latitudes,  and  possessing  slower  motion,  would  act 
as  a  brake,  arresting  the  excessive  velocity,  and  thus  for- 
ever preventing  an  excess  of  centrifugal  momentum. 

(1.)  R&ason  and  observation  affirm  t/te  probability  of 
a  ring. — Laplace,  who  looked  as  profoundly  as  any  one  into 
the  physical  principles  involved,  was  of  a  different  opin- 
ion. And  so  have  been  nearly  all  writers  on  the  subject. 
If  contraction  of  total  volume  takes  place,  the  sum  of  the 
radii  vectores  of  the  particles  must  be  diminished,  and 
then,  if  the  principle  of  conservation  of  areas  is  not  falla- 
cious, the  velocity  of  rotation  must  be  increased.  (See  p. 
106.)  The  increase  must  sooner  or  later  exceed  the  limit 

*Rev.  S.  Parsons,  Methodist  Quarterly  Jtevieir,  January,  1877;  Rev.  W.  B. 
Slaughter:  The  Modern  Genesis,  ch.  iv—  a  mechanically  absurd  objection. 


OBJECTIONS   FROM  COMETS,  STARS  AKD   NEBULA.  187 

of  equilibrium  between  centripetal  and  centrifugal  tenden- 
cies, to  whatever  extent  progress  toward  that  limit  may 
be  retarded  by  the  transfer  of  particles  from  higher  lati- 
tudes toward  the  equator.  The  denial  of  the  conclusion  is 
met  by  the  rings  of  Saturn  and  the  annular  nebulae,  by 
the  rings  of  Plateau,  and  even  by  the  projection  of  water 
from  a  rapidly  revolving  grindstone. 

(2.)  M.  FayJs  objection  considered, — M.  Faye  has  also 
raised  the  objection  that  under  such  conception  of  the  con- 
stitution of  the  primordial  mass  as  was  entertained  by  La- 
place, annulation  would  never  occur.*  The  idea  of  Laplace 
was,  as  M.  Faye  states  it  \  "that  the  sun  is,  except  as  to 
incandescence,  a  globe  similar  to  our  own,  solid  or  liquid, 
surrounded  by  an  atmosphere.  This  atmosphere,  enriched 
without  doubt  by  certain  materials  more  volatile  than  the 
others,  was  formerly  expanded  through  the  influence  of 
original  heat,  as  far  as  the  orbit  of  the  remotest  planet,  the 
velocity  of  rotation  of  the  central  globe  being  propagated 
through  the  successive  layers  by  means  of  their  mutual 
friction,  in  such  a  manner  as  to  bring  into  perfect  agree- 
ment the  rotation  of  the  atmosphere  and  that  of  the  cen- 
tral globe.  Through  the  influence  of  cooling  the  central 
globe  contracted  by  degrees;  its  velocity  of  rotation,  and 
consequently  that  of  the  atmosphere,  underwent  progres- 
sive acceleration.  But  there  is  a  limit  which  the  accelera- 
tion of  the  atmosphere  could  not  surpass;  it  is  that  where 
the  equatorial  centrifugal  force  was  equal  to  gravity;  all 
outside  of  this  ceases  to  belong  to  the  atmosphere,  and 
ought  to  begin  a  planetary  revolution  about  the  sun.  But 
here,  one  thing,  it  seems  to  me,  is  forgotten.  If  the  cen- 
tral globe  contracts  by  degrees,  through  cooling,  so  should 
the  atmosphere.  But  nothing  proves  that  it  will  not  con- 
tract so  much  as  not  to  attain  the  limit  just  stated.  It 

*  M.  Faye,  Comptes  Rendus,  torn,  xc,  p.  571. 
t  Compare  Part  IV,  ch.  iv,  of  the  present  v/ork. 


188  ORIGIN    OP   THE   SOLAR   SYSTEM. 

would  suffice  that  to  an  augmentation  of  one  thousandth 
in  the  velocity  of  rotation  of  the  central  globe  should  cor- 
respond a  contraction  of  one  and  a  half  thousandths  in  the 
radius  of  the  atmosphere,  to  cause  that  the  latter  should 
never  part  with  any  portion,  and  thus  should  never  give 
place  to  the  formation  of  a  planet.* 

"Modern  studies  have  caused  us  to  reject  this  concep- 
tion. For  us,  the  mass  of  the  sun  is  in  a  state  of  fluidity 
more  or  less  complete  in  all  its  extent.  There  exists  no 
solid  or  liquid  surface  which  marks  the  commencement  of 
an  atmosphere.  That  which  we  call  the  photosphere  is 
only  the  region  where  the  progressive  lowering  of  the  in- 
ternal temperature  permits  certain  vapors  temporarily  to 
condense  and  form  a  shifting  zone  of  incandescent  clouds. 
If,  then,  in  former  times,  the  sun  possessed  a  greater  vol- 
ume, its  entire  mass  must  have  been  expanded,  and  the 
entire  mass  must  have  undergone  contraction  through  the 
influence  of  refrigeration." 

*  If  r  and  /•'  represent  the  equatorial  radius  of  the  "atmosphere"  at  two 
consecutive  epochs,  and  have  such  values  that  »•'  =  >•-  —  ;  and  if  6  and  6'  repre- 
sent the  angular  velocities  of  the  "central  body"  (and  by  hypothesis,  also  of 

the  atmosphere)  at  the  same  two  epochs,  and  have  such  values  that  0'  =  0  -\ ; 

then  the  value  of  the  centrifugal  tendency  on  the  equator  of  the  atmosphere  at 
the  two  epochs  will  be  r  0*  and  r'  0™,  and  the  condition  of  no  augmentation  of 
this  tendency  is  expressed  by  equating  these  two  values.  Substituting  the 
equivalents  of  r'  and  0',  the  equation  becomes 


whence  m  =  ±   \'  n  (n  —  1 )  4-  n  —  1. 

If  m,  the  denominator  of  the  fractional  increase  of  the  angular  velocity,  be  taken 
at  1,000,  then  n  =  500  very  nearly.  That  is,  if  the  angular  velocity  of  the  central 
body  is  increased  T^'un,  a  corresponding  decrease  of  TTHITJ  '»  the  radius  of  the 
atmosphere  would  preserve  the  centrifugal  tendency  unchanged,  and  no  part  of 
the  atmosphere  would  be  abandoned.  This  result,  it  will  be  noticed,  assumes 
that  all  the  motion  of  the  atmosphere  is  imparted  by  the  rotation  of  the  central 
body,  and  that  the  contraction  of  the  atmosphere  (which  under  the  conception 
stated  would  be  much  more  than  that  of  the  central  liquid  or  solid  central  body) 
contributes  nothing  to  the  increase  of  its  velocity.  While  M.  Faye's  reasoning 
is  correct,  it  is  extremely  doubtful  whether  his  premises  express  correctly  the 
conception  of  Laplace. 


OBJECTIONS   FROM    COMETS,  STARS    AND   NEBULA.  189 

So  far  M.  Faye's  objection  rests  only  against  an  alleged 
particular  conception  of  Laplace.  It  is  true  that  Laplace 
employs  language  which  might  justify  such  an  interpreta- 
tion of  his  ideas  as  is  set  forth  by  M.  Faye.  That,  how- 
ever, is  of  little  consequence,  since  those  who  hold  to  a 
nebular  evolution  of  planets  are  not  limited  to  methods  of 
detail  which  seemed  satisfactory  to  astronomers  of  the 
last  century.  Annulation  under  the  Laplacean  conception 
may  be  impossible,  and  yet  both  possible  and  probable 
under  the  modern  conception  of  the  solar  constitution, 
and  of  the  primordial  nebular  condition  of  the  matter  of 
our  system. 

But  M.  Faye  next  proceeds  to  show  by  mathematical 
reasoning  that  a  sun  constituted  according  to  the  modern 
conception  would  never  annulate  bv  the  simple  process  of 
equilibrated  equatorial  zones.*  I  am  persuaded,  however, 
that  errors  have  crept  into  his  investigation,  which  vitiate 
his  conclusion.  However  presumptuous  it  may  appear  to 
criticise  the  work  of  a  mathematician  of  such  masterly 
skill,  it  is  certainly  the  privilege  of  every  one  to  compare 
his  conclusions  with  facts,  and  to  scrutinize  the  tenability 
of  his  assumptions.  The  facts  of  the  actual  world  con- 
vince us  of  the  possibility  of  annulation  through  augmen- 
tation of  centrifugal  tendency.  The  orbital  velocities  of 
the  planets  are  still  such  that  centrifugal  and  centripetal 

*  The  general  formula  which  he  employs  to  express  the  density  of  the  nebu- 
lar mass  at  any  point  whatever  is 

where  D  represents  the  central  density,  R  the  radius  of  the  solar  [nebular]  equa- 
tor, r  the  distance  from  any  point  whatever  to  the  centre,  n  an  arbitrary  positive 
number,  and  a  a  very  small  fraction.  This  gives  a  very  feeble  final  density  [that 
is,  when  r  becomes  equal  to  R],  and  at  the  same  time  a  decrease  of  density  as 
rapid  as  may  be  desired,  from  the  centre  to  the  surface,  since  n  may  vary  from 
zero  to  infinity,  and  a  may  be  replaced  by  zero,— a  supposition  which  makes  the 
surface  density  zero.  This  law,  M.  Faye  remarks,  is  analogous  to  that  which  M. 
Roche  (Essai  sur  I'origine  du  systeme  solaire,  1873)  has  employed  with  full 
cess  for  the  terrestrial  globe,  and  to  that  of  Legendre  and  Laplace. 


uc- 


190 ORIGIN   OF   THE   SOLAR   SYSTEM. 

tendencies  are  equalized;  and  simple  calculation  shows 
that  a  heated  nebulous  mass,  under  certain  conditions  of 
internal  density,  beginning  contraction  with  an  initial 
rotation  however  slow,  will  acquire  increase  of  rotational 
velocity  up  to  the  point  of  annulation.*  Moreover,  M. 
Faye,  in  approaching  his  conclusion,  assumes  as  one  con- 
dition, that  "we  do  not  admit  the  planets  formed  at  the 
expense  of  the  sun,"  an  assumption  which  conflicts  not 
only  with  our  own  nebular  theory,  but  also  with  that 
subsequently  expounded  by  M.  Faye  himself. f  He  thus 
finds  the  moment  of  inertia  constant  in  all  the  history  of 
the  sun's  contraction.  Again,  in  determining  the  numeri- 
cal ratio  of  the  centrifugal  tendency  to  the  central  attrac- 
tion, he  obtains  the  value  of  certain  quantities  from  the 
present  condition  of  the  sun.  Among  these  is  the  rota- 
tional velocity  of  the  sun.  This,  I  have  elsewhere  main- 
tained, is  an  erroneous  assumption,  since  we  discover  valid 
reasons  for  concluding  that  the  actual  solar  rotation  is  not 
fully  and  simply  the  result  of  that  secular  acceleration  to 
which  we  ascribe  the  action  of  ring-making. 

I  conclude,  therefore,  that  we  have  good  physical 
grounds  for  maintaining  that  in  a  highly  heated,  nebulous 
rotating  spheroid,  increase  of  angular  velocity  would  pro- 
ceed to  such  a  limit  that  annulation  would  begin. 

*  Let  6  and  9'  represent  the  angular  velocities  of  the  nebula  at  commence- 
ment of  contraction  and  at  an  epoch  when  annulation  is  possible,  and  r  and  r' 
represent  the  equatorial  radii  of  the  nebula  at  the  same  epochs.  To  find  what 
amount  of  contraction  is  necessary  to  increase  the  primitive  angular  velocity  6 

to  »',  we  have 

6  .  e,  ..  rn  .  r«, 

whence  r>  =  ±r\    £• 

If  9=1  and  0'=4,  r'=y2  r.  Generally,  if  6'=m  0.  then  r'=r  ,—.  That  is,  the 
annulnting  radius  varies,  in  different  cases,  inversely  as  the  square  root  of  the 
ratio  of  the  primitive  and  annulnting  angular  velocities,  and  is  equal  to  the 
primitive  radius  multiplied  by  the  reciprocal  of  the  square  root  of  that  ratio. 
Now  it  is  manifestly  allowable  to  suppose  such  a  law  of  variation  of  internal 
density  that  while  0  increases  to  0',  r  may  decrease  to  r'. 

t  See  §  8  of  the  present  chapter. 


OBJECTIONS   FROM    COMETS,  STARS   AND   NEBULA.  191 

The  whole  discussion  may  be  supplemented  by  the  sug- 
gestion that  the  initial  rotary  velocity  of  the  nebula  may 
be  rapid.  It  arises,  according  to  the  views  here  set  forth, 
from  some  primitive  nebular  collisions.  Whatever  rotary 
momentum  may  be  thus  imparted  will  be  conserved  during 
subsequent  contraction;  and  increase  of  rotary  velocity 
will  proceed  from  this  beginning.  We  are  at  liberty  to 
assume  any  such  initial  velocity  of  rotation  as  would 
necessitate  annulation  at  any  subsequent  stage. 

4.  The  want  of  uniformity  in  the  composition  of  the 
fixed  stars. — Mr.  Rutherford,  in  concluding  a  statement 
of  results  of  the  spectral  examination  of  stars,  says:* 
"We  have  long  known  that  'one  star  differeth  from  an- 
other star  in  glory';  we  have  now  the  strongest  evidence 
that  they  also  differ  in  constituent  materials  —  some  of 
them,  perhaps,  having  no  elements  to  be  found  in  some 
other.  What,  then,  becomes  of  that  homogeneity  of 
original  diffuse  matter  which  is  almost  a  logical  necessity 
of  the  nebular  hypothesis?"  To  this  it  may  be  replied: 

(1.)  No  such  universal  and  absolute  homogeneity  is 
assumed.  It  is  not  admitted  that  even  our  solar  nebula 
was  completely  homogeneous.  If  we  discover  identical 
substances  in  other  orbs,  that  is  a  fact  pointing  toward  an 
ancient  material  connection  or  common  origin;  but  if  we 
find  evidence  of  some  unknown  substances,  that  is  not 
sufficient  to  negate  the  significance  of  so  many  facts 
pointing  to  a  common  cosmical  history;  it  is  rather  what 
ought  to  be  expected  where  the  different  parts  of  the 
material  system  are  separated  by  intervals  so  immense. 

(2.)  The  indications  from  spectroscopic  observations 
are  yet  too  incomplete  and  too  ambiguous  to  base  any 
important  negations  on;  but  so  far  as  stellar  spectra  have 
anything  to  testify,  they  tend  wonderfully  to  establish  the 
unity  of  substance  throughout  the  visible  universe. 

*  Rutherford,  Amer.  Jour.  Sci.,  II,  xxxv,  77. 


192  ORIGIN    OF   THE   SOLAE    SYSTEM. 

5.  The  spectra  of  the  nebulae  do  not  indicate  sufficient 
pressure.* — It  is  in  this  assumed  that  the  nebular  theory 
implies  that  the  various  nebulre  should  be  in  all  stages  of 
condensation;  and  hence,  as  different  degrees  of  conden- 
sation give  bright  spectral  lines  of  different  breadths, 
some  of  the  nebular  spectra  should  afford  broad  lines. 
But  as  Mr.  Plummer  says:  "From  the  observations  of 
Huggins  it  would  appear  that  the  bright  lines  in  the  nebu- 
lar spectra  present  no  appreciable  thickness  in  all  those 
cases  in  which  it  has  been  possible  to  use  a  narrow  slit. 
The  lines  have  invariably  been  found  to  be  exceedingly  fine. 
Hence,"  continues  Mr.  Plummer,  "we  are  furnished  with 
distinct  proof  that  the  gases  so  examined  are  not  only  of 
nearly  equal  density,  but  that  they  exist  in  a  very  low 
state  of  tension.  This  fact  is  fatal  to  the  nebular 
theory.'1''  This  is  a  most  surprising  example  of  inductive 
generalization.  Only  a  few  suggestions  are  required. 

(1.)  The  nebular  theory  primarily  and  chiefly  concerns 
the  origin  of  the  bodies  of  the  solar  system  from  a  sup- 
posed primitive  nebula.  The  phenomena  of  firmamental 
nebulas  have  been  summoned  to  illustrate  and  confirm  the 
theory;  but  if  it  should  be  proved  that  such  confirmation 
is  wholly  unattainable,  the  theory  would  still  rest  on  all 
the  analogies  and  physical  relations  which  Laplace  and 
many  others  have  accepted  as  adequate  ground  of  convic- 
tion. 

(2.)  It  seems  impossible  that  any  unbiased  judgment 
should  hesitate  to  detect  in  the  aspects  of  the  nebulae  the 
evidence  of  the  reality  of  their  close  relation  to  such  a  form 
and  condition  of  matter  as  the  nebular  theory  of  planetary 
origin  postulates.  But  the  bright  lines  which  they  yield 
are  not  broad  enough!  Well,  for  all  that,  the  bright  lines 
declare  that  the  nebulae  are  gaseous,  or  at  least  contain 

*  Plummer,  Nalural  Science  Review,  1875;  Kcv.  8.  Parsons,  Me.th.  Quur.Jiev., 
Jan.  1877,  pp.  138-9. 


OBJECTIONS   FROM    COMETS,  STABS   AND   NEBULA.  193 

gases,  and  that  they  are  self-luminous,  and  their  narrow- 
ness proclaims  a  high  state  of  rarefaction.  Here  are 
three  sentences  of  favoring  testimony  to  oppose  to  one  of 
unfavorable  testimony.  Let  us  see  what  that  fourth  sen- 
tence is  worth.  A  nebula  would  not  be  a  nebula  unless  it 
were  tenuous  and,  in  free  space,  so  little  condensed  as  to 
yield  narrow  lines.  Has  Mr.  Plummer  tried  the  effect  of 
compressing  a  bit  of  nebula  in  a  confined  space,  to  see  if 
its  spectral  lines  would  not  widen?  Next,  the  interior  of 
the  nebula  is  the  region  where  tension  must  exist;  but 
the  light  upon  which  Huggins  experimented  came  neces- 
sarily from  the  exterior,  where,  by  the  laws  of  gaseous 
bodies,  the  tension  must  always  be  at  a  minimum. 

(3.)  If  nothing  more  were  to  be  said,  the  certainty  of 
the  inferences  drawn  from  width  of  spectral  lines  is  not 
yet  sufficiently  well  established  to  outweigh  the  general 
evidences  that  the  nebulae  are  of  such  nature  as  has  been 
commonly  ascribed  to  them;  still  less  to  render  nugatory 
the  hundreds  of  indications  manifested  in  the  solar  system 
that  our  planets  and  satellites  have  had  a  nebular  origin. 
Neither,  finally,  can  the  assumed  identification  of  elemen- 
tary substances  in  the  nebulae  be  regarded  as  sufficiently 
certain  to  base  on  them  any  destructive  criticism  of  the 
nebular  theory.  The  correspondences  of  the  spectral  lines 
are  not  exact,  and  the  inferences  are  merely  provisional. 
The  nebulae  may  in  fact  exist  in  a  state  of  elemental  dis- 
sociation; and  even  our  recognized  elements  may  occur  in 
the  nebulae  in  that  state  of  ultimate  decomposition  into 
simple  and  universal  world-stuff  toward  which  our  atten- 
tion has  been  directed  by  so  many  modern  investigators 
(see  p.  48).  In  such  case,  the  spectral  lines  would  be  pro- 
duced under  circumstances  such  as  have  not  been  created 
in  our  laboratories,  and  it  would  be  impossible  for  us  at 
present  to  give  them  a  correct  interpretation. 

So  far  then,  as  nebular  spectra  testify  at  all,  they  indi- 
13 


194  ORIGIN    OF   THE   SOLAR   SYSTEM. 

cate  a  wonderful  range  of  common  conditions  between  the 
nebulas  and  the  sun,  and  tend,  like  stellar  spectra,  to  estab- 
lish the  unity  of  substance  throughout  the  visible  universe, 
as  also  unity  of  fundamental  conditions  and  unity  of 
dynamical  activities. 

I  think  I  have  thus  gathered  together  most  of  the  ob- 
jections offered  in  recent  times,*  to  the  theory  of  the 
nebular  origin  of  the  solar  system.  Very  few  of  these 
have  been  offered  by  scientists  who  have  looked  intelli- 
gently into  the  physical  relations  of  the  assumed  nebulous 
matter  during  the  progressive  cooling.  The  objections 
offered  by  this  class  relate  only  to  matters  of  detail.  The 
most  numerous  objections  have  been  urged  by  those  least 
competent  to  criticise,  and  by  such  have  been  paraded  with 
greatest  ostentation  and  most  defiant  dogmatism.  Many 
of  the  objections  admitted  in  the  foregoing  list  are  so 
truly  frivolous  that  I  have  noticed  them  only  to  forestall 
the  pretence  that  "  numerous  difficulties  remain  unre- 
moved." 

*  An  anonymous  writer  (North  American  Review,  xcix,  1-33,  July,  1864)  has 
thrown  aside  the  nebular  theory  as  being  only  "  a  happy  guess,"  and  though  con- 
forming to  observed  phenomena  as  alleged,  deriving  more  support  from  its  char- 
acter as  a  developmental  hypothesis  in  harmony  with  the  hypothesis  of  organic 
development,  than  from  any  sufficient  ground  for  "the  fundamental  assumption 
of  a  nebulous  matter."  This  writer  recedes  to  the  Aristotelian  conception  of 
"an  infinite  and  endless  variety  of  manifestations  of  causes  and  Jaws,  without  a 
discoverable  tendency  on  the  whole."  It  is  quite  astonishing  that  the  recognition 
of  order  and  unity  in  the  method  of  the  universe  should  be  met,  in  some  minds,  by 
such  a  feeling  of  repugnance,  while  order,  method  and  unity  are  the  normal  and 
necessary  expressions  of  intelligence —of  that  Supreme  Intelligence  in  whose 
defence  they  unconsciously  stultify  themselves.  A  finite  intelligence  does  not 
exercise  its  high  and  characteristic  attributes  by  a  helter-skelter  and  immethodi- 
cal  production  of  results;  but  deems  it  first  of  all  essential  to  fix  upon  a  plan 
under  which  its  whole  range  of  action  shall  be  adjusted  and  unified. 

The  account  of  the  "nebular  hypothesis  "  by  Professor  R.  A.  Proctor,  in  the 
last  edition  of  the  American,  Cyclopcedia,  unites  the  fundamental  conception  of 
Laplace  with  some  of  the  fanciful  suggestions  of  Spencer,  and  is  completed  with 
some  of  the  characteristic  features  of  the  meteoric  theory  maintained  by  the 
anonymous  writer  laxt  referred  to.  For  an  intelligent  account  of  the  nebular 
theory,  see  an  article  by  Prof.  John  Lc  Conte  in  Pop.  Sci.  Monthly,  April,  1873, 
650-60. 


OBJECTIONS    FROM   COMETS,  STARS   AND    NEBULAE.  195 

The  reader  will  notice  that  in  many  cases,  several  differ- 
ent admissible  suggestions  are  offered  to  meet  a  single 
alleged  difficulty.*  This  results  from  the  fruitfulness  of 
the  physical  conditions  attending  the  nebular  evolution. 
Many  different  modes  of  action  for  the  production  of  a 
particular  result  are  possible,  and  their  conditional  predica- 
tion is,  therefore,  perfectly  legitimate.  It  is  not  to  be 
alleged  that  we  are  at  a  loss  to  assign  physical  explanations 
for  the  phenomena  which  we  witness;  or  that  our  expedi- 
ents are  conflicting.  Our  inability  to  indicate  specifically 
and  categorically  which  of  several  possible  modes  of  action 
has  produced  a  given  result,  arises  from  the  impossibility 
of  knowing  the  value  of  certain  factors  in  the  problem, 
which  would  be  conditioned  bv  concomitant  circumstances 
belonging  to  the  history  of  the  remote  past.  Especially 
must  we  always  remain  in  ignorance  of  the  amount,  direc- 
tion and  epochs  of  perturbative  influences  exerted  by 
masses  of  matter  not  involved  in  the  transformations  of 
our  solar  nebula.  It  is  perfectly  legitimate  to  assume  that 
these  have  acted  in  such  way  as  to  produce  the  phenomena 
attributable  to  perturbations. 

If,  then,  one  or  more  rational  explanations  is  offered 
for  every  assignable  condition  or  phenomenon  in  our  sys- 
tem, it  is  only  an  undiscerning  judgment  which  can  con- 
tinue to  allege  a  conflict  between  facts  and  the  nebular 
theory;  and  in  view  of  the  large  array  of  coincidences 
with  the  facts  which  no  competing  theory  has  ever 
attempted  to  explain,  it  would  seem  to  argue  a  callous- 
ness to  evidence  to  persist  in  denunciation  of  the  funda- 
mental conception  as  a  physical  explanation  of  the  origin 
and  history  of  our  system. 

*  Still  further  explanations  of  difficulties  are  afforded  by  the  theory  of  cos- 
mic tides,  and  these  will  be  indicated  in  connection  with  the  exposition  of  tidal 
actions  and  reactions  (Part  II,  ch.  ii,  §  6). 


196  ORIGIN    OF   THE   SOLAR   SYSTEM. 

§  7.    WHAT  THE  NEBULAR  THEORY  DOES  NOT  IMPLY 

It  is  probably  within  the  truth  to  say  that  much  oppo- 
sition to  the  theory  has  been  aroused  by  a  mistaken  inter- 
pretation of  its  consequences.  I  desire,  therefore,  to  state 
concisely  what  the  truth  of  the  nebular  theory  does  not 
imply. 

1.  It  is  not  a  theory  of  the  evolution  of  the  Universe. 

—  It  is  primarily  a  genetic  explanation  of  the  phenomena 
of  the  solar  system;  and  accessorily  a  coordination  in  a 
common  conception,  of  the  principal  phenomena   in   the 
stellar  and  nebular  firmament,  as  far  as  human  vision  has 
been  able  to  penetrate. 

2.  It  does  not  regard  the  Comets  as  involved  in  that 
particular  evolution  which  has  produced  the  Solar  System; 

—  but  it  recognizes  the  comets  as  forms  of  cosmic  exist- 
ence coordinated  with  earlier  stages  of  nebular  evolution. 

3.  It  does  not  deny  an  antecedent  history  of  the  lumi- 
nous fire-mist. —  It  makes  no  claim  to  having  reached  an 
absolute  beginning.  The  fire-mist  may  have  previously 
existed  in  a  cold,  non-luminous  and  invisible  condition. 
It  may  have  emerged  from  the  substance  of  the  ethereal 
medium,  or  may  have  no  consubstantial  relation  with  it. 
The  fire-mist  and  other  nebulae  may  consist  of  matter  in  a 
state  of  molecular  division,  or  in  aggregates  of  any  mass. 
Other  nebulae  may  be  intensely  heated  and  in  a  state  of 
chemical  dissociation,  or  their  luminous  phenomena  may 
arise  from  a  condition  of  things  unknown  to  terrestrial 
science.  We  only  affirm  that  the  primitive  nebula  from 
which  our  system  was  evolved  possessed  at  a  certain  stage 
the  physical  properties  of  an  intensely  heated  and  highly 
tenuous  vapor. 

4.  It  does  not  profess  to  discover  the  ORIGIN"  of  things, 
but  only  a  stadium  in  material  history, —  Its  starting 
point  postulates  matter  and  energy.  It  makes  no  affirma- 


WHAT  THE    NEBULAR   THEORY    DOES    NOT   IMPLY.  197 

tion  concerning  the  origin  of  these.  It  leaves  the  philoso- 
pher and  the  theologian  as  free  as  they  ever  were  to  seek 
the  origin  of  the  modes  of  being.*  It  glimpses  matter  in 
a  certain  phase  of  existence,  having  active  forces  within, 
impelling  it  along  an  intelligible  and  methodical  career  of 
development.  It  stands  on  the  regularity  of  nature  and 
writes  a  history  revealed  to  the  understanding.  Matter 
and  force  are  recognized  as  existing  realities;  but  in  refer- 
ence to  their  subjective  nature  the  theory  is  as  silent  as 
upon  their  origin. 

5.  It  does  not  deny  the  existence  O/"PLAN  and  PURPOSE 
in  the  system  of  cosmic  evolution. —  It  insists  that  the 
plan  is  so  fixed  that  the  most  confident  calculations  as  to 
the  future  and  past  may  be  based  upon  it.  It  holds  that 
the  concomitant  existences  and  the  successive  stages  in 
the  whole  history  are  intelligibly  adjusted  to  each  other; 
and  as  it  is  a  system  of  phenomena  and  events  which 
human  thought  can  grasp  and  contemplate,  it  is  itself, 
philosophically  considered,  the  expression  of  thought,  and 
implies  a  Thinker  possessing  attributes  as  vast  as  the  ere- . 
ation.  Moreover,  there  is  nothing  in  the  scientific  postu- 
lates or  implications  of  the  theory  to  contravene  the  affir- 
mation that  as  the  product  of  intelligence  it  must  of 
necessity  involve  purpose',  and  as  the  force  which  existed 
in  the  beginning  and  is  the  moving  principle  through  all 
the  history  cannot  be  conceived  as  active  without  a  sub- 
ject, nor  as  residing  in  an  undiscerning,  unthinking,  invol- 
untary subject,  so  the  whole  history  of  cosmical  evolution 
is  a  display  as  wide  as  the  universe  and  as  enduring  as 
time,  of  the  ever-present  activity  of  an  Intelligent  Person- 
ality controlling  and  effectuating  all  the  operations  of 
nature. 

*  "  The  problem  of  existence  is  not  resolved.  *  *  *  The  nebular  hypothe- 
sis throws  no  light  upon  the  origin  of  diffused  matter.  *  *  *  The  nebular 
hypothesisimpliesaFirstCau.se  *  *  *  " — (H.  Spencer,  Westminster  Re- 
view, Ixx,  127,  July,  1858.) 


198  ORIGIN"    OF   THE   SOLAR   SYSTEM. 

In  the  light  of  these  statements,  I  desire  to  reproduce 
the  opening  paragraph  of  a  review  penned  by  a  theologian 
whose  profession,  and  whose  creditable  acquaintance  with 
science  should  equally  have  restrained  him  from  commit- 
ting himself  to  a  sentiment  so  divergent  from  the  facts 
and  so  disparaging  to  the  interests  of  religion.  I  leave  the 
paragraph  as  food  for  reflection.  It  is  as  follows: 

"Since  the  speculations  of  the  evolutionists  have  been 
advanced  with  such  boldness  and  plausibility,  the  nebular 
hypothesis  has  assumed  an  importance  which  it  did  not 
possess  in  the  time  of  Herschel  and  Laplace.  It  is,  in 
fact,  the  first  link  in  the  development  theory  by  which  it  is 
attempted  to  bind  together  all  nature  in  a  rigid  system  of 
materialism,  forever  excluding  the  interposition  of  mind 
and  the  idea  of  a  divine  cosmos.  Final  cause  is  pronounced 
a  chimera,  and  the  first  great  cause  is  remanded  to  the 
sphere  of  the  unknown."* 

§  8.  PROPOSED  MODIFIED  FORMS  OF  NEBULAR  THEORY. 

1.  M.  Faye's  proposed  modification. — It  is  indispens- 
able, in  a  general  discussion  of  nebular  cosmogony,  to 
make  adequate  mention  of  some  important  modifications 
in  the  theory  of  world-genesis  which  have  lately  been 
offered  by  the  distinguished  Director  of  the  Observatory 
at  Paris.  As  these  are  applied  by  the  author  especially 
to  the  cosmogonic  history  of  our  system,  rather  than  to 
nebular  evolutions  at  large,  the  present  is  perhaps  the 
most  appropriate  place  for  reproducing  his  views.  I  shall 
translate  the  greater  part  of  his  article  in  the  "  Comptes 
Rendus,"  on  the  Origin  of  the  Solar  System.-\ 

"The  hypothesis  of  Laplace  is  based  on  the  preexist  - 
ence  of  a  globe  possessing  all  the  mass  of  the  solar  system, 

*  Rev.  8.  Parsons,  M.A.,    The  Nebular  Hypothesis  and  Modern    Genesis, 
Methodist  Quarterly  Review,  IV,  xxix,  127,  Jan.  1877. 
t  Comptes  Rendw,  xc,  637,  March  22,  1880. 


PROPOSED  MODIFIED  FORMS  OF  NEBULAR  THEORY.  199 

and  all  its  mechanical  energy  under  the  form  of  rotation. 
Through  the  action  of  an  intense  heat  whose  origin  is  not 
explained,  the  atmosphere  of  this  globe,  for  to  him  it  was 
only  an  atmosphere,  became  expanded  to  the  limits  of  the 
remotest  planetary  orbit  of  our  system.  In  cooling,  it 
abandoned  from  time  to  time,  in  the  plane  of  the  primitive 
equator,  the  materials  of  the  planets.  Under  this  new 
form,  the  primitive  energy  subsists  unimpaired,  but  now 
wholly  in  the  circulations  which  we  find  existing.  Thus 
by  the  intervention  of  heat  and  the  play  of  centrifugal 
force,  Laplace  caused  to  be  produced  a  totally  different 
distribution  of  the  mass  and  of  its  movements.  This  corres- 
ponds, to  a  certain  point,  with  what  we  see.  But  this 
intervention  of  heat  is  itself  a  pure  hypothesis.  To 
justify  it,  we  must  suppose  with  Poisson  that  there  are  in 
the  universe,  regions  with  very  different  temperatures, 
and  that  the  primitive  globe,  by  virtue  of  its  motion  of 
translation,  had  passed  into  one  of  the  hottest.(l)  * 

"Observation  leads  us,  meanwhile,  toward  other  ideas. 
The  nebulae,  where  matter  is  disseminated  over  vast  spaces, 
have  always  produced  in  us  and  other  astronomers  the 
conviction  that  they  are  the  point  of  departure  of  evolu- 
tions very  various,  and  resulting  in  ultimate  formations 
the  most  diverse,  such  as  simple  suns,  double,  triple  and 
quadruple  suns,  and  globular  masses  of  minute  suns 
reckoned  by  thousands.  It  is  necessary  to  contemplate 
the  scene,  on  a  fine  evening,  with  the  aid  of  a  good  teles- 
cope, under  the  guidance  of  an  experienced  astronomer 
who  has  had  the  goodness  to  select  beforehand  appropriate 
objects.  The  spectator  finds  himself  then  in  the  presence 
of  a  series  of  forms  so  varied  —  at  first  rudimentary,  then 
more  and  more  evolved  —  in  the  position  of  a  naturalist 
passing  through  a  forest,  embracing  in  a  glance  of  the 

*  Numerals  in  parenthesis  refer  to  observations  at  the  end  of  this  Section. 
The  foot-notes  are  by  the  present  writer. 


200  ORIGIN  OF   THE   SOLAR   SYSTEM. 

eye,  the  phases  in  the  life  of  the  same  existence,  although 
these  phases  demand  in  reality,  for  each  tree,  a  long  series 
of  years  Is  it  not  natural  to  be  inspired  by  these  facts, 
so  much  the  more  as  our  own  system  appertains  to  the 
type  the  most  common,  and  the  easiest  to  comprehend, 
that  of  a  nebulosity  at  first  vague,  then  presenting  a 
central  condensation,  being  absorbed  little  by  little, 
regularly,  into  a  nebulous  star,  and  finally  into  a  single 
sun  in  the  dark  depth  of  the  sky?  Thus  heat  would  no 
longer  appear  as  an  exterior  agent  which  must  be  invoked 
arbitrarily.  We  see  it  develop  itself  by  degrees  at  certain 
points  of  the  nebulosity  as  a  result  of  the  energy  proper 
to  a  vast  dissemination  of  materials  exerting  a  mutual 
attraction  at  a  distance.  This  is  then  a  natural  phase  in 
the  series  of  phenomena.  We  might  even  conceive  an 
anterior  state  where  the  disseminated  matter  may  have 
remained  a  long  time  dark  and  cold.  The  marvellous 
indications  of  spectral  analysis,  and  the  mechanical  theory 
of  heat  fully  confirm  this  method  of  viewing  the  subject. 

"Suppose,  for  the  purpose  of  fixing  these  ideas,  that 
the  matter  of  our  system  had  been  thus  disseminated  in 
the  beginning,  in  a  spherical  space  having  a  radius  a 
hundred  times  greater  than  that  of  the  orbit  of  Neptune. 
Viewed  at  the  distance  of  the  planetary  nebula  whose 
parallax  Dr.  BrUnnow  has  ventured  to  measure,  this  very 
year,  at  the  Irish  observatory  at  Dunsink,  ours  would 
appear  with  a  diameter  of  only  5'.  The  density  of  the 
matter,  supposing  it  continuous,  would  be  two  hundred 
and  fifty  thousand  million  [250,000,000,000]  times  less 
than  that  of  a  receiver  with  a  vacuum  of  one  thousandth.* 


*I  subjoin  the  following  calculation: 

Let  d  =  mean  density  of  matter  of  solar  system,  that  of  the  earth  being  1. 
.    a  =  its  volume,  that  of  the  earth  being  1, 
p  =  its  density  when  expanded  as  described, 
R=  earth's  radius, 
r  =  radius  of  the  supposed  sphere. 


PROPOSED  MODIFIED  FORMS  OF  NEBULAR  THEORY.  201 

Its  temperature  would  be  in  the  neighborhood  of  absolute 
zero,  at  an  epoch  when  the  stars  now  visible  could  not  yet 
have  been  formed.  In  spite  of  this  inconceivable  tenuity, 
the  attraction  of  the  entire  mass  would  be  felt  none  the 
less  in  all  its  parts.  Any  molecule  whatever  circulating 
at  the  surface  would  have  a  velocity  only  ten  times  less 
than  that  of  Neptune.*  In  the  interior,  the  attraction  of 
the  entire  mass  goes  on  decreasing  toward  the  centre  just 
in  the  ratio  of  the  distance  to  that  point,  and  realizes 

Then,  since  the  density  of  the  matter  is  inversely  as  its  volume,  we  have 
p  :  d ::  a|irRS  :  ±nr*  ::  a  R»  :  r*, 

whence  p=— r-acf. 

r    r* 

To  find  d,  we  may  add  together  the  masses  of  the  principal  bodies  of  the 
solar  system  (See  Annuaire  du  Bureau  des  Longitudes,  1881,  p.  135),  giving  324,- 
877.923,  and  also  the  volumes,  giving  1,285,833.272  (this  being  the  value  of  a),  the 
earth  being  the  unit  of  mass  and  volume ;  then  dividing  total  mass  by  total  vol- 
ume, we  get  mean  density  in  reference  to  the  earth,  .2526  (which  is  only  .0004 
less  than  the  mean  density  of  the  sun  alone).  As  the  specific  gravity  of  the 
earth  is  5.66,  and  that  of  water  in  reference  to  air  is  773.28  (A)inuaire,  p.  514,)  we 
have 

d=.2526  X  5.66  X  773.28=1106.79. 

Also  r=2, 775,000,000  X  100=2775  X  108,  and  R=3959; 

whence  p=  (3959)3  X  1,285,&33.272  X  1106.79 

(2775)3  X  1024 


This  is  the  density  of  the  matter  compared  with  common  air  (which  is 
14.435  times  the  density  of  hydrogen).  The  density  compared  with  air  exhausted 
to  one  thousandth  is  .000000000004226.  Unity  divided  by  this  fraction  gives  236? 
600,000,000,  which  expresses  the  density  of  air  exhausted  to  one  thousandth,  com- 
pared with  the  density  of  the  matter  of  the  solar  system  when  expanded  to  a 
sphere  having  100  times  the  diameter  of  Neptune's  orbit.  The  Sprengel  air-pump 
exhausts  to  one  millionth,  and  yet  the  air  remaining  in  the  receiver  has  236,- 
600,000  times  the  density  of  the  matter  of  the  solar  system  when  expanded  as 
supposed.  Further,  the  matter  beyond  the  sphere  of  Neptune,  supposing  the 
distribution  uniform,  would  have  been  a  million  times  the  amount  of  matter 
within  that  sphere,  which  is  14.419,000,000  times  less  than  M.  Faye's  supposition 
makes  it.  This  shows  an  immensely  greater  tenuity  of  the  extra-Neptunian 
matter,  or,  what  is  much  more  probable,  a  more  limited  extension  of  the  matter. 
If  the  matter  extended  only  as  far  as  Neptune's  orbit,  its  density  was" a  million 
times  greater,  or  .000000004226  compared  with  common  air,  or  .000000061  compared 
with  hydrogen. 

*  If  v  and  v'  represent  the  velocities  at  Neptune  and  on  the  periphery  of  the 
nebula,  and  r  and  r'  the  radii  of  revolution,  then  by  the  principle  of  equal  areas, 

V*  :  V»  ::  r' :  r,  whence  t»»=t>»  L^,*!  =  *JL,  and  v'=~v. 


202  ORIGIN    OF   THE    SOLAR    SYSTEM. 

thus,  temporarily,  it  is  true,  that  is,  so  long  as  the  homo- 
geneity of  the  nebula  shall  endure,*  an  abstract  concep- 
tion of  central  forces,  the  consequences  of  which  have 
been  discussed  in  treatises  on  mechanics  since  the  time 
when  Newton  signalized  it  as  a  law  fully  as  capable  of 
binding  harmoniously  the  movements  of  a  system  as  that 
of  gravity  varying  in  the  inverse  ratio  of  the  square  of 
the  distance.  At  that  time  all  bodies  placed  within  that 
vast  circumference  would  describe,  under  the  slightest 
impulse,  ellipses  or  circles  having  their  centre  at  the 
centre  of  the  nebula,  f  For  all  these  bodies  the  period  of 
revolution  would  be  the  same,  a  thousand  times  greater 
than  that  of  Neptune.  J  A  molecule  falling  from  any  point 
whatever  toward  the  centre  would  reach  it  in  a  quarter  of 
that  time,  that  is  to  say,  in  41,000  years. 

"  This  nebula  moves.  We  find  in  the  translation  of  the 
sun  toward  the  constellation  Hercules,  the  movement  of 
its  centre  of  gravity.  The  total  movement  must  be  more 
complex,  and  embrace  a  slow  rotation  or  rather  a  sort  of 
whirlpool  motion  of  the  whole  mass  around  a  certain  axis, 
as  in  the  nebulne  of  Lord  Rosse.  But  it  is  only  in  the 
plane  centrally  perpendicular  to  this  axis  that  these  rota- 
tions could  become  regular  and  persistent,  because  there 

*  The  principle  would  not  be  disturbed  by  any  rate  of  increase  of  density, 
provided  it  proceeded  symmetrically  on  all  sides  at  corresponding  distances  from 
the  centre. 

tSee  Tail  and  Steele's  Dynamics  of  a  Particle,  4th  ed.,  114. 

$  Orbital  velocities  are  always  proportional  to  the  central  force.  Therefore, 
if  v,  r  and  t  represent  the  velocity,  distance  and  time  of  any  revolving  body,  then 
since  in  this  case  velocities  are  proportional  to  the  distances  and  inversely  as  the 

times,  we  may  take  ni\  nr  and—  to  represent  the  velocity,  distance  and  time  of 
any  other'body  revolving  as  assumed.  Therefore,  —  =  —  =y  or  -  =  -  .'.  n  =  1, 

and  n  t=t ;  so  that  the  times  of  revolution  of  all  bodies  moving  as  supposed  would 
be  equal.  But  the  times,  under  the  law  of  gravity,  are  as  the  cubes  of  the  square 

roots  of  the  distances ;  and  for  the  distances  r  and  100  r,  are  as  1  to  lOOf,  or  as  1 
to  1000.  Hence  the  uniform  time  of  revolution  would  be  a  thousand  times  the 
period  of  Neptune. 


PROPOSED  MODIFIED  FORMS  OF  NEBULAR  THEORY.  203 

they  would  adjust  themselves  according  to  the  same  laws 
as  a  circulation  regulated  by  the  proper  gravity  of  the  sys- 
tem, that  is  to  say,  of  all  the  parts.  If,  then,  trains  of 
matter  somewhat  circular,  in  a  word,  rings  like  those  of 
Saturn,  or  those  of  certain  nebulae,  such  as  51  Messier, 
become  finally  established  in  the  bosom  of  the  nebula  (2),  in 
the  vicinity  of  the  primordial  equator,  the  velocity  must 
have  increased  from  the  internal  border  of  each  ring  to 
the  external,  proportionally  to  the  distance  from  the  cen- 
tre, as  in  the  case  of  the  rotation  of  a  solid  ring. 

"All  the  planets  proceeding  from  the  rupture  of  these 
rings  would  continue  to  circulate  in  the  primitive  direc- 
tion, which  we  will  call  <J.irf-<-t.  Here  is  the  capital  fact  of 
which  the  hypothesis  of  Laplace  takes  so  good  account. 
Only,  their  rotations  should  all  be  direct,  if  things  re- 
mained in  this  state.  But  from  the  commencement,  I 
mean  to  say  from  the  time  when  this  nebula  became  com- 
pletely isolated,  there  has  been  produced  a  phenomenon 
which  has  modified  these  first  conditions.  From  all  the 
regions  which  do  not  participate  in  these  regular  circula- 
tions, the  materials  of  the  nebula  fall  toward  the  centre, 
describing  very  elongated  ellipses  (3),  and  not  circles.  They 
produce  there  a  gradual  progressive  condensation,  in  such 
a  way  that,  disregarding  a  multitude  of  partial  movements, 
the  density  of  the  nebula  ceases  to  be  uniform,  and  finally 
arrives  at  a  regular  rate  of  increase  from  the  surface  to 
the  centre.'" 

M.  Faye  next  proceeds  to  determine  the  direction  of 
the  rotation  in  this  nebulous  mass  at  different  distances 
from  the  centre,  and  deduces  an  expression  for  the  veloci- 
ty which  at  certain  distances  from  the  centre  gives  direct 
motion;  at  greater  distances,  a  diminished  velocity  in  the 
same  direction;  at  a  certain  greater  distance,  no  motion, 
and  at  all  distances  still  greater,  a  retrograde  motion  con- 


204  ORIGIN    OF   THE    SOLAR   SYSTEM. 

tinuing  to  increase  in  velocity  to  the  surface.*  "Thus,"  he 
says,  "  the  nebula  during  the  entire  period  of  concentration 
is  divided  into  two  regions  very  different:  (ft)  The  exterior, 
where  the  rings  in  giving  birth  to  planets,  will  impress 
upon  them  a  retrograde  rotation,  like  that  of  Uranus  or 
Neptune;  (b)  The  interior,  where  the  planets  will  all 
have  a  direct  motion,  like  Saturn,  Jupiter,  etc.  This  is 
the  singular  phenomenon  which  our  system  presents,  and 
against  which  the  hypothesis  of  Laplace  opposes  itself 
(4).  It  is  thus  bound  to  a  simple  increase  of  density  from 
the  border  to  the  centre  of  the  nebula.  Without  doubt 
things  might  happen  otherwise.  If  the  rings  had  a  pre- 
ponderant mass,  they  would  attract  to  themselves  all  the 
matter,  and  would  finally  vacate  the  central  regions,  as  in 
the  nebula  of  the  Lyre. 

"  The  system  thus  formed  is  by  no  means  complete.  It 
occupies  at  first  a  space  much  greater  than  our  actual  sys- 
tem; but  in  subsequent  times,  central  condensation  continu- 
ally progresses,  not  by  cooling,  be  it  well  understood,  but 
by  the  continued  action  of  gravity.  The  planetary  orbits 
were  at  first  plunged  in  the  diffused  and  rare  mass  of  the 
nebula.  By  degrees  this  mass  withdrew  from  the  regions 
exterior  to  the  orbits,  and  proceeded  to  concentrate  in  the 
interior,  toward  the  centre  of  these  same  orbits.  The 
areas  described  in  a  given  time  in  these  circulations  will 
not  for  this  reason  change,  but  the  rings  or  the  planets 

*  The  expression  adopted  for  the  law  of  density  (see  also  p.  128)  is 

D('-M<i) 

The  square  of  the  linear  velocity  of  the  circulatory  movement  is 


An  inspection  of  the  factor  in  parenthesis  shows  that  with  increase  of  r  the 
negative  term  increases  more  rapidly  than  the  positive  term.  While  it  remains 
smaller,  the  value  of  the  whole  expression  is  positive,  and  this  denotes  direct 
motion;  when  it,  equals  the  first  term,  the  value  of  the  whole  expression  is 
zero,  and  when  it  exceeds  the  first  term,  the  whole  expression  hecomes  negative, 
which  means  that  the  direction  of  the  motion  is  retrograde. 


PROPOSED  MODIFIED  FOKMS  OF  NEBULAR  THEORY.  205 

will  gradually  approach  the  centre,  and  their  velocity  will 
be  continually  accelerated,  conformably  to  the  theory 
which  Laplace  has  given  in  the  fourth  volume  of  the 
Mifiinique  Celeste,  for  the  inverse  case  where  the  central 
mass  goes  on  diminishing.  Here  we  are  not  concerned 
with  minute  effects,  since  it  is  almost  the  entire  mass  of 
the  nebula,  up  to  about  YTJJ>  which  marches  thus  in  space 
from  orbit  to  orbit,  to  gather  itself  at  the  centre.  To  this 
is  added  another  cause,  which  acts  exactly  in  the  same 
manner,  that  is  to  say,  the  resistance  of  the  materials 
which  constantly  travel  through  space,  and  fall  almost 
directly  toward  the  sun,  and  from  nearly  all  sides.  It  is 
further  evident  that  this  double  and  continual  contraction 
of  the  orbits  will  proceed,  without  altering  in  any  respect 
the  direction  of  the  rotation  of  the  planets  or  the  direction 
of  the  circulation  of  their  satellites.' 

"As  to  the  distances  of  the  planets  from  the  sun,  or  of 
the  satellites  from  their  planets,  nothing  prevents  that 
they  should  be  found  to-day,  beyond  the  limits  assigned 
by  Laplace.  There  is  no  more  question,  in  fact,  in  causing 
to  intervene  here  the  play  of  centrifugal  force  for  pro- 
ducing some  at  the  expense  of  others. 

"We  have  assumed  that  the  sun  absorbed  all  that 
which  was  not  involved  in  the  circulation  of  the  rings  in 
the  vicinity  of  the  primitive  equator.  This  could  not  be 
completely  the  case.  A  portion  of  the  superficial  nebu- 
losities, especially  toward  the  poles,  actuated  by  very  feeble 
lateral  impulsions  through  the  influence  of  various  causes, 
and  describing  around  the  centre  very  elongated  ellipses, 
must  have  been  able  to  traverse  the  central  regions  with- 
out being  arrested  there.  Escaped  from  the  agglomera- 
tion where  the  sun  at  a  later  period  is  formed,  they  have 
nevertheless  experienced  its  action  in  numerous  returns, 
and  must  have  continued  to  describe  elongated  trajectories, 
variable  in  form  and  position,  whose  final  term  will  be  an 


206  OKIG1X    OF   THE   SOLAR    SYSTEM. 

ellipse  having  its  focus  in  the  place  where  the  primitive 
ellipse  had  its  centre.  Undoubtedly,  here  is  presented  the 
difficulty  of  the  rapid  contraction  which  the  circular  orbits 
have  undergone;  but  as  these  portions  move  in  elongated 
ellipses,  reaching  or  even  passing  the  limits  of  the  nebula, 
they  must  have  escaped  almost  completely  this  effect,  since 
one  part  of  their  orbits  lay,  since  their  origin,  beyond  the 
region  whence  the  mass  withdrew  (5).  The  period  of 
revolution  must  have  remained  very  considerable,  and 
must  have  been  reckoned  by  thousands  of  years,  as  in  the 
primitive  times.  As  to  the  direction  of  the  movement,  it 
will  be  indifferently,  direct  or  retrograde;  the  inclination 
of  the  planes  of  the  orbits  to  the  primitive  equator  will  be 
any  value  whatever;  in  a  word,  this  will  be  the  realm  of 
the  comets,  which  appertain  so  visibly  to  the  solar  system, 
though  the  hypothesis'  of  Laplace  would  be  compelled  to 
exclude  them. 

"However  it  may  be  on  this  delicate  point,  our  system 
became  stable  from  the  epoch  when  that  part  of  the  nebula 
not  involved  in  the  planets  became  entirely  absorbed  in 
the  sun.  The  void  has  been  made  complete,  as  about  the 
simple  or  double  stars  which  we  see  in  a  dark  night.  It 
remains  to  expend  the  energy  transformed  into  heat;  but 
that  which  has  conserved  the  method  of  the  movement 
will  remain. 

"This  conservation,  nevertheless,  is  not  absolute.  At- 
tractions provoke  in  all  bodies  internal  strains  which 
develop  a  little  heat.  Cometary  masses  passing  near  the 
sun  disintegrate  into  nebulous  trains  as  if  for  return  to 
their  origin.  These  latter  proceed  to  collide  with  planets 
and  engender  there  light  and  heat.  Thus  disappears  by 
degrees  a  portion  of  the  store  of  mechanical  energy  but 
this  is  only  a  feeble  image  of  the  past. 

"It  remains  to  restore  to  the  starting  point  this  mys- 
terious dissemination  of  dark  matter  which  contains  in 


PROPOSED  MODIFIED  FORMS  OF  XEBULAB  THEORY.  207 

potentiality  so  many  wonders;  but  this  must  remain  the 
insuperable  term  which  we  meet  in  all  questions  of  origins. 
Nevertheless,  the  possibility  cannot  be  denied.  The  re- 
pulsive force  of  the  sun  which  I  have  attributed  to  the 
action  of  incandescent  surfaces,  and  where  other  astrono- 
mers see  the  play  of  electric  forces,  produces  before  our 
eyes,  in  the  extremely  divided  matter  of  comets,  though  in 
miniature,  a  dissemination  entirely  parallel. 

"  I  ask  for  this  rapid  exposition,  the  indulgence  of  the 
Academy,  for  I  am  sensible  how  far  it  is  from  the  incom- 
parable precision  which  we  admire  in  the  hypothesis  of 
Laplace.  Since  the  latter  was  formulated,  the  two  Her- 
schels  with  their  powerful  telescopes,  the  American  as- 
tronomers with  their  gigantic  lenses,  have  taught  us  to 
read  the  heavens  better.  Spectral  analysis  and  thermody- 
namics have  been  created.  In  short,  Laplace  was  unac- 
quainted with  the  new  conditions  which  observation  has 
continued  to  reveal  to  us  down  to  the  most  recent  times. 
I  have  thought  that  the  moment  had  arrived  for  attempt- 
ing to  bring  all  these  facts  into  coordination."* 

It  will  be  noticed  that  most  of  the  fundamental  assump- 
tions of  this  theory  are  in  accord  with  the  positions  taken 
in  this  work.  That  the  different  nebulas  are  destined  to 
different  methods  of  evolution  I  have  maintained  in  the 
first  chapter.  The  likeness  of  the  stellar  firmament  to  the 
assemblage  of  variously  aged  trees  in  a  forest  is  an 
analogy  pointed  out  by  Laplace.  I  have  argued,  and  so 
has  Mr.  Croll,  that  the  heat  of  incandescent  nebulae  may 
be  the  result  of  the  transformation  of  mechanical  energy; 
and  I  have  pointed  out  reasons  for  presuming  that  incan- 
descent nebulous  matter  existed  previously  in  a  cold  and 
dark  state.  M.  Faye  does  not  hesitate  to  recognize  with 

*  See  also  M.  Faye's  Note  sur  les  idees  cosrnogoniqaes  de  Kant,  a  itropos 
d'une  reddfnation  de  prionte  de  M.  Schlotel,  Comptes  Rendus,  xc,  1246,  May  31, 


208  OKIGIST    OF   THE    SOLAR   SYSTEM. 

Laplace,  that  nebular  equatorial  rings  will  undergo  disrup- 
tion, though  the  rings  are  conceived  by  him  to  be  formed 
within  the  nebular  mass,  and  not  at  its  periphery.  The 
descent  of  the  parts  of  the  nebula  toward  the  centre  by 
virtue  of  their  own  gravitation,  is  a  doctrine  generally 
admitted,  though  M.  Faye  assumes  that  other  neighboring 
parts  are  not  thus  moved.  That  the  whole  nebula  might 
be  transformed  into  a  ring  is  a  conclusion  which  I  have 
enunciated,  and  on  different  grounds.  M.  Faye  recognizes 
the  influence  of  meteoroidal  matter  in  condensation,  and 
the  production  of  heat  and  light  by  collision  with  the 
planets;  and  is  the  first  after  the  present  writer,  so  far  as 
known,  to  suggest  that  attractions  "provoke  internal 
strains  which  develop  a  little  heat;"  though  his  statement 
is  a  single  sentence,  and  does  not  reveal  any  high  estimate 
of  the  theoretical  importance  of  the  principle. 

At  the  same  time,  however,  M.  Faye's  noteworthy 
modification  of  nebular  cosmogony  embodies  some  state- 
ments and  principles  on  which  I  would  like  to  offer  a  few 
special  observations: 

(1.)  The  circumstance  that  Laplace  offered  no  explana- 
tion of  the  heat  postulated  in  the  primitive  nebula  ought 
not  to  weigh  against  the  plausibility  of  his  theory.  As  M. 
Faye  observes,  we  always  arrive  sooner  or  later  at  questions 
of  origins  which,  for  the  time  being,  must  remain  unan- 
swered. M.  Faye  himself  has  assumed  more  unexplained 
conditions  than  Laplace.  If  the  latter  finds  evidence  of 
the  primitive  existence  of  intense  heat,  its  inexplicability 
is  no  greater  evidence  against  its  reality  than  the  mystery 
of  the  aurora  borealis  against  the  reality  of  that  pheno- 
menon. Nor  was  Laplace  consigned  to  the  alternative  of 
accepting  Poisson's  hypothesis.  He  may  have  rejected  it 
as  improbable,  and  have  trusted  to  the  future  to  disclose  a 
physical  cause  of  the  heat.  Poisson's  hypothesis  was  not 
reached  by  an  unbroken  process  of  scientific  deduction;  it 


PROPOSED  MODIFIED  FORMS  OF  XEBULAR  THEORY.  209 

was  a  hypothesis  created  outright  by  the  power  of  inven- 
tion. The  incandescent  nebula  of  Laplace  was  a  state  dis- 
closed to  intelligence  by  a  rational  regressive  process  of 
argumentation. 

(2.)  As  to  the  establishment  of  rings  "  in  the  bosom  of 
the  nebula,"  it  will  be  noticed  that  M.  Faye  does  not  assert 
the  probability  of  its  occurrence,  or  mention  any  physical 
ground  on  which  it  could  be  predicated,  but  simply  says, 
"if  they  should  become  finally  established,"  the  angular 
velocity  would  be  the  same  on  both  borders.  Now  a  spiral 
motion,  as  I  have  conceived,  implies  a  retarding  influence 
exerted  upon  the  exterior  portions  of  a  fluid  in  a  state  of 
rotation.  While  a  fluid  mass  possessing  a  spiral  motion 
must  tend  toward  a  symmetrically  spheroidal  form,  the 
production  of  our  annulus  can  only  be  a  peripheral  inci- 
dent; and  it  is  certain  that  we  know  of  no  physical  cause 
for  its  existence  except  that  assigned  by  the  theory  of 
Laplace.  A  "  whirlpool "  motion  may  be  considered  to 
differ  in  direction  from  the  spiral  motion  here  contemplated. 
The  paths  described  have  the  same  form,  but  the  parts 
converge  by  a  winding  progress  toward  the  centre.  They 
are  conceived  as  descending  by  a  retarded  motion  at  the 
same  time  that  some  impulsion  has  deflected  them  from 
direct  lines  to  the  centre.  Admitting  that  "trains"  of 
particles  might  be  able  to  extricate  and  isolate  themselves 
sufficiently  from  the  opposing  friction  of  contiguous  regions 
of  particles,  so  as  to  flow  like  streams  in  the  ocean,  with  a 
differentiated  and  special  motion;  admitting  also,  that  the 
nebula  as  a  whole  possesses  some  rotary  motion,  and  that 
the  rate  of  this  increases  as  the  parts  descend  nearer  the 
centre,  what  can  we  infer  on  physical  grounds,  as  to  the 
formation  of  rings  ?  We  cannot  look  for  them  as  a  result 
of  motion  toward  the  centre;  thi-s  tends  continually  to  pre- 
vent rings.  We  cannot  expect  them  to  result  from  local 
tangential  impulsions  producing  currents  which  flow  around 
14 


210  ORIGIX    OF   THE    SOLAR   SYSTEM. 

the  mass;  for  by  hypothesis,  circumferential  motion  is  all 
the  time  combined  with  motion  of  descent;  and  besides, 
the  differential  motion  of  such  currents  would  be  destroyed 
by  friction,  and  the  currents  would  cease  to  exist;  and 
finally,  if  they  should  persist,  the  planes  of  the  paths  de- 
scribed would  sustain  no  common  relation  to  a  fixed  plane. 
Rotation  of  the  mass  would  exert  no  influence  upon  the 
trains  of  particles  except  through  the  development  of  cen- 
trifugal tendencies.  These  would  be  greatest  at  remoter 
distances  from  the  axis  of  rotation,  that  is,  in  the  regions 
where  the  linear  motion  under  the  law  of  attraction  within 
a  sphere  would  be  greatest.  In  other  words,  the  greatest 
velocity  of  descent  would  be  opposed  by  the  greatest  con- 
trary tendency;  the  motion  in  the  descending  spiral  would 
be  somewhat  equalized,  and  the  form  of  the  spiral  would 
more  nearly  approach  a  circle.  Now,  it  is  conceivable  that 
the  relative  amount  of  the  centrifugal  tendency  might 
become  so  great  that  the  motion  of  descent  would  be 
practically  zero,  and  a  train  at  the  equator  would  pass  into 
the  form  of  a  ring.  But  such  ring  results,  it  will  be 
noticed,  from  a  suspension  of  the  motion  of  descent,  which 
is  a  cardinal  conception  in  M.  Faye's  theory  at  this  point, 
and  also  in  relation  to  cometic  genesis;  and  assumes  the 
controlling  influence  of  the  centrifugal  tendency.  In  both 
these  requirements  the  conditions  of  annulation  become 
exactly  those  assumed  in  the  Laplacean  theory.  It  is  not 
affirmed  that  M.  Faye  reasons  or  would  reason  in  this  way 
in  following  out  the  genesis  of  a  ring.  He  does  not 
explain  by  what  physical  action  a  ring  would  arise;  and 
all  that  is  here  stated  is  that  if  a  ring  could  come  into  ex- 
istence in  a  "whirlpool"  nebula,  it  would  be  only  through 
centrifugal  action,  and  must  be  peripheral  and  equatorial, 
as  Kant  and  Laplace  assumed.  Thus,  when  M.  Faye's 
theory  is  pushed  through  the  details  of  ring-genesis,  its 


PROPOSED  MODIFIED  FORMS  OF  NEBULAR  THEORY.  211 

peculiarities  avail  nothing,  and  it  invokes  the  Laplacean 
principle  to  carry  on  the  cosmogonic  work. 

(3.)  It  is  not  apparent  that  portions  of  matter  falling 
from  the  regions  of  the  poles  of  the  nebula  through  a 
medium  in  which  attraction  varies  as  the  distance  from 
the  centre,  would  necessarily  describe  "elongated  ellipses." 
Though  this  is  a  correct  physical  principle,  and  might  be 
realized  in  a  hollow  sphere,  it  would  not  be  within  a 
nebulous  sphere.  The  descending  matter  would,  from  the 
assumed  homogeneity  of  the  nebula,  possess  a  physical 
state  somewhat  similar  to  that  of  the  matter  passed 
through.  Its  motion  would  therefore  be  retarded  by  fric- 
tion, and  approximated  to  the  motion  of  the  medium  by 
which  it  might  be  surrounded.  But  supposing  those 
elliptic  motions  accomplished,  any  condensation  of  the 
nebula  arising  from  the  motion  of  these  portions  of  matter 
toward  the  centre  would  be  neutralized  by  the  succeeding 
motion  of  the  same  portions  of  matter  away  from  the 
centre.  This  is  not  to  deny  that  condensation  would  take 
place,  but  only  that  the  existence  of  "  elongated  elliptic 
orbits"  would  contribute  to  condensation.  The  "regular 
rate  of  increase "  of  density  toward  the  centre  would 
result  from  the  consentaneous  movement  of  parts  from  the 
more  peripheral  regions  along  lines  more  or  less  disturbed, 
toward  the  centre  of  gravity  of  the  mass. 

(4.)  On  M.  Faye's  reasoning  to  establish  the  necessity 
of  retrograde  motions  in  the  parts  of  the  system  remotest 
from  the  centre,  I  have  had  occasion  to  offer  some  observa- 
tions in  another  place.*  I  have  also  attempted  to  show 
that  by  properly  supplementing  the  Laplacean  conception, 
retrograde  motions  are  provided  for  as  well  as  direct  mo- 
tions. 

(5.)  M.  Faye's  speculation  concerning  the  origin  of 
comets  seems  particularly  inconclusive.  He  undertakes 

*  Part  I,  Chap.  II,  §  4,  2;  and  Part  II,  Chap.  I,  §  2,  1,  (4). 


212  ORIGIN   OF   THE   SOLAR   SYSTEM. 

in  the  first  place,  a  task  unnecessarily  imposed,  since  it 
may  be  rationally  maintained  that  the  comets  are  not 
native  members  of  our  system.  He  proceeds,  in  the  next 
place,  in  a  wholesale  and  incautious  way  to  consider  the 
cometary  masses  as  parts  of  the  nebula,  and  then  speaks 
of  them  as  "reaching  or  even  passing"  the  limits  of  the 
nebula,  and  next  states  that  "  one  part  of  their  orbits  lay 
since  their  origin,  beyond  the  region  whence  the  mass 
irithdreio."  The  self-contradiction  here  is  palpable,  and 
becomes  a  physical  absurdity  when  we  reflect  that  M. 
Faye  attributes  to  an  origin  within  the  original  limits  of 
our  nebula,  cometary  masses  which  retire  to  enormous 
distances  beyond  any  supposable  limits  reached  by  the 
primitive  nebula,  and  even  traverse  our  system  with  velo- 
cities greater  than  could  be  acquired  by  the  action  of 
central  forces  native  to  the  system. 

While,  therefore,  deeply  impressed  by  the  learned 
ingenuity  of  M.  Faye's  modification  of  nebular  cosmogonv, 
I  do  not  as  yet  feel  prepared  to  give  it  a  preference  over 
that  based  on  strict  Laplacean  conceptions. 

2.  Spiller's  Proposed  Modification. —  It  seems  desirable 
also  to  notice  a  modification  of  nebular  theory  advanced 
by  Spiller  of  Berlin.*  He  dissents  from  the  theory  of  the 
formation  of  planets  through  the  intervention  of  rings. 
According  to  his  view  planets  are  the  product  of  tidal 
action  combined  with  centrifugal  tendency.  This  action 
is  exerted  upon  the  central  mass  after  reaching  the  con- 
dition of  igneous  fluidity.  It  is  manifest  that  a  separated 
planetary  mass  must  produce  a  tidal  swell  of  some  magni- 
tude upon  the  fluid  central  mass.  This  tide  would  be 
turned  always  in  the  direction  of  the  planet — an  antitide 

*Philipp  Spiller:  Die  Wfltschojtfung  vom  Standpunke  d-r  heutigen  Wissen- 
schaft.  Mil.  neaen  Untersiichungen,  1868,  2d  ed.  1873;  Die  En/stehung  der  Welt 
itnd  die  Einheit  der  Naturkrtifte.  Populdre  Kosmogonie.  See  also  the  same 
writer's  important  work.  Die  Vrkraft  des  Wellalls  nachifirem  Wesen  und  Wirken 
ien  Naturgebieten.  Fiii-  Gebildele  jeden  Stand«»,  374pp.  Berlin,  1879. 


PKOPOSED  MODIFIED  FORMS  OF  XEBULAR  THEORY.  213 

moving  simultaneously  on  the  opposite  side.  It  is  manifest 
also  that  the  magnitude  of  the  tide  would  increase  with 
the  proximity  of  the  planet,  arid  still  further  with  the  con- 
junction of  two  or  more  planets.  At  some  perihelion  of 
the  planet,  therefore,  —  concurring  perhaps  with  a  conjunc- 
tion of  planets  —  the  centrifugal  tendency  of  the  equatorial 
portion  of  the  central  fluid  mass  would  exceed  gravitation, 
and  the  tidal  swell  would  be  lifted  bodily  from  connection 
with  the  central  mass  and  move  centrifugally  to  such  dis- 
tance that  a  state  of  equilibrium  would  be  reached.  The 
mass  thus  detached  would  at  once  assume  a  spheroidal 
planetary  form.  Thus  it  is  supposed  Uranus  was  detached 
as  a  tidal  swell  raised  by  the  attraction  of  Neptune;  Sat- 
urn, by  a  similar  action  of  Uranus,  and  so  on.  As  to 
Neptune,  it  must  be  admitted  that  the  separation  took 
place  solely  through  the  tangential  momentum  at  the 
equator  of  the  original  mass,  or  it  must  be  presumed  that 
a  tidal  effect  was  produced  by  the  presence  of  some  ex- 
ternal body.* 

This  theory  possesses  the  merit  of  explaining  the  ellip- 
ticity  of  the  planetary  orbits  as  a  primary  result,  and  of 
dispensing  with  rings  and  thus  avoiding  the  problem  of 
planetation  from  rings.  But  on  the  contrary  it  encounters 
great  difficulties.  It  is  necessary  to  show  the  probability 
of  the  non-formation  of  rings  during  the  nebulous  stage, 
or  else  to  explain  their  subsequent  disappearance  without 
the  production  of  planetary  bodies.  It  is  also  necessary  to 
show  that  the  central  mass  ever  possessed  such  velocity  of 
rotation  as  to  detach  a  tidal  swell  from  a  liquid  spheroid  —  a 
difficulty  increased  by  the  comparative  insignificance  of  such  ' 
a  swell  on  a  body  possessing  the  relative  mass  of  the  sun. 
But  the  greatest  difficulty  is  presented  by  the  fact  that 

*  The  reader  will  note  that  Spiller's  conception  is  the  prototype  of  Mr.  G. 
H.  Darwin's  (noticed  hereafter)  concerning  the  retirement  of  the  lunar  mass 
from  the  semi-fluid  earth. 


214  OEIGIN    OF   THE   SOLAK   SYSTEM. 

the  sun  has  not  yet  attained  a  liquid  condition,  according 
to  the  views  of  modern  astronomers,  and  there  is  no  likeli- 
hood that  its  temperature  had  subsided  to  any  lower  point 
than  the  present  at  any  epoch  in  the  past.  While  there- 
fore, Herr  Spiller  has  offered  a  theory  which  is  thinkable 
and  consistent  with  the  laws  of  nature,  it  does  not  seem 
to  be  one  which  represents  the  actual  history  of  nature.* 

*  The  writer  intended  to  notice  the  seemingly  important  work  of  M.  Roche, 
entitled  Svr  I' origins  du  Syateme  Solaire,  published  by  Gauthier-Villars,  Paris, 
1873,  but  though  ordered  repeatedly  from  booksellers  in  Paris,  Berlin  and  Leipzig, 
no  copy  of  it  has  been  obtained. 


CHAPTER  II. 

GENERAL    COSMOGONIC     CONDITIONS 
ON    A    COOLING    PLANET. 


•Und  ob  Alles  im  ewigen  Wechsel  Kreist 

Es  beharret  im  Wechsel  eiu  ruhiger  Geist.— SCHILLER. 

Opinionum  commenta  delet  dies,  naturae  judicia  confirmat. 

CICEKO,  de  Nat.  Deor. 


§  1.   RELATIVE  AGES  OF  PLANETS  IN  A  SYSTEM. 

ACCORDING  to  the  nebular  theory  here  accepted, 
!•£»*-  the  ages  of  the  planets  must  be  graduated  according 
to  their  distances  from  the  sun.  The  remotest  planet  at 
present  known  is  Neptune.  Its  existence,  before  discovered, 
was  pointed  out  by  certain  perturbations  in  the  next  interior 
planets,  which  were  not  fully  accounted  for  by  the  attrac- 
tions of  any  known  body.  There  still  remain  some  residual 
disturbances  which  have  led  to  the  conjecture  that  a  still 
remoter  planet  exists.  This  opinion  was  shared  by  my 
late  honored  colleague,  Professor  James  C.  Watson.  For 
similar  reasons  Mercury  for  many  years  has  been  doubt- 
fully regarded  as  the  most  interior  planet.  Dr.  Lescarbault 
announced  that  such  planet  had  actually  fallen  under  his 
observation,  and  he  designated  it  Vulcan.  But  other  ob- 
servers were  not  able  to  verify  the  alleged  discovery. 
During  the  total  eclipse  of  July  29,  1878,  Professor 
Watson,  in  charge  of  observations  in  Wyoming,  devoted 
his  entire  attention  to  the  search  for  intra-Mercurial  planets, 
and  succeeded  in  satisfying  himself  that  one  or  two  came 

215 


216  A    COOLING    PLANET. 

within  the  range  of  his  instrument.*  Professor  Lewis 
Swift  also  reported  from  Denver  some  similar  observa- 
tions.f  The  great  difficulty  of  exact  determinations  during 
the  few  seconds  of  totality  of  an  eclipse,  and  the  absence 
of  other  corroborative  observations,  have  led  many  astron- 
omers to  adhere  to  the  opinion  that  Professors  Watson 
and  Swift  mistook  fixed  stars  for  planets. 

But  the  stage  of  development  of  a  planet  does  not 
depend  alone  on  its  age.  Planetary  evolutions  rest  finally 
on  progressive  cooling.  The  condition  of  a  planet  as  a 
whole  is  determined  by  the  temperature  of  the  mass. 
After  incrustation,  the  state  of  the  surface  depends  less 
and  less  upon  the  temperature  of  the  interior,  since  the 
rate  of  conduction  of  interior  heat  through  the  crust  con- 
tinually diminishes.  But  a  large  mass,  other  things  being 
the  same,  retains  a  high  temperature  longer  than  a  smaller 
one.  A  small  planet  may  become  totally  refrigerated, 
while  a  large  one  of  greater  age  may  linger  in  a  state  of 
self-luminosity.  The  length  of  time  the  heat  of  a  planetary 
body  will  endure,  depends,  then,  on  mass  and  extent  of 
radiating  surface.  As  the  ratio  of  the  masses  is  greater 
than  that  of  the  surfaces,  the  relative  length  of  time  a  par- 
ticular phase  will  endure  is  greater  than  is  indicated  by 
the  relative  masses  of  the  planets.  In  other  words,  if  one 
planet  has  twice  the  mass  of  another,  their  densities  being 
the  same,  the  duration  of  a  certain  phase  of  cooling'  will 
be  more  than  twice  as  long  as  in  the  other.J 

*  See  his  communications  inAmer.  Jour.  Sci.  Ill,  xvi,  230-3,  310-13,  Sept.  and 
Oct.,  1878. 

t  L.  Swift,  Amer.  Jour.  Sd.  Ill,  xvi,  313-15.  See  also,  Science,  26  Feb.  and 
23  Apr.  1881. 

t  If  A  and  A'  represent  the  rates  of  radiation  of  two  planets,  r  and  r',  their 
radii,  H  and  II'  the  total  heat  in  the  two,  and  p  and  p'  their  respective  densities; 
then  since  the  rates  of  radiation  are  as  the  surfaces, 


And  since  the  total  amounts  of  heat  are  as  the  masses, 
H  :  H'  ::  pr3  :  p'r'3  ;  .'.  II' 


PASSAGE   TO   THE   MOLTEN    PHASE.  217 

§  2.   PASSAGE  TO  THE  MOLTEN  PHASE. 

A  planetary  body  is  to  be  conceived  as  existing,  at  a 
certain  epoch,  in  a  state  of  fire-mist.  In  this  state  a  por- 
tion of  the  matter  exists  in  minute  liquid  particles  which 
are  held  in  suspension  in  the  gases  which  constitute  the 
remaining  portion.  Some  chemical  compounds  probably 
exist,  but  others,  evidently,  are  still  prevented  by  the 
intense  heat  from  forming.  The  gases,  deeply  seated 
beneath  the  surface,  are  subjected  to  an  enormous  pres- 
sure which  reduces  them  to  a  density  approaching  that  of 
the  liquefied  material,  or  even  exceeding  it.  At  some 
epoch  the  molten  matter  must  descend  toward  the  centre 
until  it  reaches  a  zone  where  its  density  is  equalled  by  the 
density  of  the  compressed  gases.  If  this  zone  of  liquid 
precipitation  is  distant  from  the  centre,  it  will  gradually 
subside  toward  the  centre,  in  proportion  as  heat  escapes 
from  the  condensed  gas,  and  it  thus  passes,  under  the 
enormous  pressure,  into  the  liquid  state.  Ultimately, 
therefore,  the  planet  will  consist  of  a  liquid  nucleus  sur- 
rounded by  an  atmospheric  fire-mist  yet  too  intensely 
heated  to  permit  all  its  constituents  to  pass  out  of  the 
aeriform  condition.  Progressively,  however,  the  atmos- 
pheric envelope  will  transfer  itself  by  precipitation  to  the 
liquefied  nucleus.  Meantime  some  portion  of  the  atmos- 
pheric constituents  will  retain  their  gaseous  condition 
below  any  temperature  which  we  have  experienced.  The 
result  will  be  a  molten  globe  surrounded  by  an  aeriform 
atmosphere. 

If  T  represent  the  relative  time  required  for  a  planet  to  pass  through  a  cer- 
tain phase  of  cooling,  then 


In  this  expression,  since  H  varies  (the  density  remaining  the  same)  as  the 
cube  of  the  radius,  and  A,  as  the  square  of  the  radius,  it  follows  that  T  varies 
more  rapidly  than  the  mass  of  the  planet.  We  may  also  deduce 


218  A   COOLING    PLANET. 

§  3.   SUPERFICIAL  SOLIDIFICATION  FROM  COOLING. 

At  a  certain  temperature  of  the  molten  sea,  certain 
compounds  will  begin  to  solidify  in  crystalline  forms. 
These  will  float  in  the  liquid  magma,  in  accordance  with 
a  principle  which  I  venture  to  regard  as  a  general  law  of 
matter.  Many  substances,  in  passing  from  a  liquid  to  a 
solid  state,  slightly  increase  in  bulk.  This  is  notoriously 
true  of  water  and  ice,  and  of  type-metal.  It  is  also  true 
that  solid  lava  floats  on  molten  lava,  a  notable  instance  of 
which  we  have  in  the  crater  of  Kilauea,  solid  glass  on 
molten  glass,  and  solid  iron  on  molten  iron.  It  is  quite 
true,  however,  that  a  piece  of  iron  may  be  taken  so  cold 
that  its  density  exceeds  that  of  molten  iron,  in  which  case 
it  will  at  first  sink.  But  after  becoming  heated  and  ex- 
panded, and  long  before  the  fusing  temperature  is  reached, 
the  iron  will  rise  to  the  surface.*  It  is  hardly  to  be 
doubted,  therefore,  that  solidification  from  cooling  would 
begin  on  the  surface  and  gradually  extend  downward,  f 

*On  floatingiron,  see  College  Gout-ant,  13  Apr.,  1872,  p,  173;  Nature,  May  10, 
1877,  23;  8  Aug.,  1878,  397,  for  conclusive  experiments;  29  Aug.  1878,  464  and  vol. 
xv i,  23.  For  Mallet's  apparently  conflicting  results,  see  Nature,  No.  156,  ab- 
stract in  Amer.  Jour.  Set.,  Ill,  viii,  212,  and  for  a  reply  to  Mallet,  see  A.  Schmidt, 
Amer.  Jour.  Set.,  Ill,  viii,  287.  Compare,  also,  Sir  William  Thomson,  Trans. 
Geol.  Soc.,  Glasgow,  vi,  40, 14  Feb.,  1878.  Some  recent  experiments  show  that 
molten  steel  has  a  specific  gravity  of  8.05,  while  cold  steel  is  7.85  (Nature,  xxvi, 
138,  Jnne  8,  1882).  On  floating  lava,  see  Scrope:  Volcanoes,  ,84,  477;  Kaemtz: 
Meteorology,  152;  G.  P.  Marsh:  Man  and  Nature,  545;  Miss  Bird:  Hawaiian 
Archipelago;  Nature,  xi,  324;  Miss  C.  F.  Gordon-Gumming:  Fire- fountains, 
the  Kingdom  of  Hawaii,  etc.,  2  vols.,  8vo.,  1883.  On  experiments  with  "  Rowley 
Rag,"  see  Chemical  News,  xviii,  191. 

tSir  William  Thomson,  nevertheless,  entertains  the  opinion  that  solidifying 
masses  would  sink  to  the  centre;  and  he  has  enunciated,  in  harmony  with  Hop- 
kins, the  somewhat  fantastic  theory  that  the  sunken  masses  would  build  up  a 
honey-combed  structure  to  the  surface,  and  "masses  falling  from  the  roofs  of 
vesicles  or  tunnels,"  might  produce  earthquake  .shocks:  Secular  Cooling  of  the 
Earth,  Trans.  Roy.  Soc.,  Edinb.,  1862;  Thomson  and  Tail's  Natural  Philosophy, 
§§  (««)»  (//);  Glasgow  Address,  1876,  Amer.  Jour.  Sci.,  Ill,  xii,  346-7;  Trans. 
Geol.  Soc.,  Glasgmo,  vi,  40-1,  14  Feb.,  1878.  In  the  latter  paper,  however,  he 
expresses  himself  with  less  confidence.  On  this  subject  see  Hopkins:  Researches 
in  Physical  Geology;  Phil.  Trans.  Roy.  Soc.,  Pt.  II,  1839,  quoted  in  his  Report  to 
British.  Assoc.,  1847,  p.  33. 


SUPERFICIAL   SOLIDIFICATION    FROM    COOLING.      219 

As  a  final  illustration,  I  venture  to  quote  from  Mr.  W. 
Matthieu  Williams*  a  description  of  what  takes  place  in 
the  "  open  hearth  finery  and  the  refining  of  pig-iron." 
"Here  a  metallic  mixture  of  iron,  silicon,  carbon,  sulphur, 
etc.,  is  simply  fused  and  exposed  to  the  superficial  action 
of  atmospheric  air.  What  is  the  result?  Oxidation  of 
the  more  oxidizable  constituents  takes  place,  and  these 
oxides  at  once  arrange  themselves  according  to  their  spe- 
cific gravities.  The  oxidized  carbon  forms  atmospheric 
matter  and  rises  above  all  as  carbonic  acid,  then  the 
oxidized  silicon  being  lighter  than  iron  floats  above  that 
and  combines  with  aluminium  or  calcium  that  may  have 
been  in  the  pig  and  with  some  of  the  iron;  thus  forming 
a  silicious  crust  closely  resembling  the  predominating 
material  of  the  earth's  crust. 

"When  the  oxidation  in  the  finery  is  carried  far  enough 
the  melted  material  is  tapped  out  into  a  rectangular  basin 
or  mould,  usually  about  ten  feet  long  and  about  three  feet 
wide,  where  it  settles  and  cools.  During  this  cooling  the 
silica  and  silicates — i.e.,  the  rock  matter — separate  from 
the  metallic  matter  and  solidify  on  the  surface  as  a  thin 
crust,  which  behaves  in  a  very  interesting  and  instructive 
manner.  At  first  a  mere  skin  is  formed.  This  gradually 
thickens,  and  as  it  thickens  and  cools,  becomes  corrugated 
into  mountain  chains  and  valleys  much  higher  and  deeper 
in  proportion  to  the  whole  mass  than  the  mountain  chains 
and  valleys  of  our  planet.  After  this  crust  has  thickened 
to  a  certain  extent,  volcanic  action  commences.  Rifts, 
dykes  and  faults  are  formed  by  the  shrinkage  of  the  metal 
below,  and  streams  of  lava  are  ejected.  Here  and  there 
these  lava  streams  accumulate  around  their  vent  and  form 
isolated  conical  volcanic  mountains  with  decided  craters, 
from  which  the  eruption  continues  for  some  time.  These 

*  Williams:  Discussions  in  Current  Science,  ch.  vii,  ''Humboldt  Library," 
No.  41,  p.  25,  Feb.,  1883. 


220  A    COOLING    PLAXET. 

volcanoes  are  relatively  far  higher  than  Chimborazo."  The 
materials  of  the  fire-formed  crust  of  a  planet  must  simi- 
larly pass  through  the  stages  of  oxidation  and  silication, 
and  the  incidents  of  progressive  cooling  must  be  fairly 
represented  by  the  phenomenon  above  described. 

§  4.  INTERNAL  SOLIDIFICATION  FROM  PRESSURE. 

While  incrustation  begins,  or  even  long  before  it  be- 
gins, solidification  may  be  produced  in  the  central  regions, 
in  a  planetary  mass  sufficiently  large,  by  the  great  pressure 
of  the  superincumbent  portions.  But  in  recognizing  the 
probability  of  a  solid  central  portion,  it  must  not  be  sup- 
posed that  the  matter  is  less  hot  than  if  a  molten  liquid. 
Any  portion  of  such  solidified  interior,  if  brought  to  the 
surface,  would  be  instantly  liquefied.  But  at  some  point 
between  the  centre  and  the  surface,  the  condensation  may 
not  be  sufficient  to  produce  solidification,  and  the  reduc- 
tion of  temperature  may  not  be  sufficient  to  cause  it. 
There  would  then  be  a  liquid  zone  interposed  between  a 
solid  crust  and  a  solid  nucleus.  That  zone  might  be  so  thin 
and  so  variable  in  its  thickness  as  to  suffer  actual  inter- 
ruption of  continuity.  It  would  then  exist  as  separate 
lakes  in  regions  more  or  less  removed  from  each  other, 
and  the  rigidity  of  the  planet  would  be  very  nearly  such 
as  is  due  to  complete  solidification.  But  even  if  a  solid 
crust  were  separated  from  a  solid  nucleus  by  a  continuous 
liquid  zone,  it  does  not  appear  to  me  that  under  the 
actions  of  the  planetary  system,  the  planet  would  be  want- 
ing in  any  of  the  astronomical  properties  of  complete 
solidity.  I  do  not  conceive  that  the  crust  would  be  likely 
to  slip  around  the  core,  since,  whatever  action  should  be 
exerted  upon  the  crust  would  be  exerted  correspondingly 
on  the  parts  beneath  the  crust.  The  several  interior  zones 
in  a  rotating  oblate  spheroid,  would  present  the  same  rela- 


MAXIMUM    INTERNAL   TEMPERATURE.  221 

tive  equatorial  protuberance  as  the  external  zone,  and 
would  all  be  moved  synchronously  and  proportionally. 

The  liquid  zone  would  not  pass  by  an  abrupt  transition 
downward  into  the  state  of  the  solid  core;  but  would  pre- 
sent gradually  increasing  degrees  of  viscosity.  The  same 
might  be  true  of  the  passage  upward  into  the  solid  crust. 

Whether  a  liquid  zone  should  exist  or  not,  it  is  ap- 
parent that  in  case  of  the  removal  or  diminution  of  the 
pressure  over  any  portion  solidified  by  pressure,  this 
would  instantly  be  followed  by  the  liquefaction  of  such 
portion.  Hence  a  deep  fissure  through  the  external  crust 
might  be  followed  by  the  passage  of  large  volumes  from 
the  solid  to  the  liquid  state.* 

§  5.  MAXIMUM  INTERNAL  TEMPERATURE  OF  AN 
INCRUSTED  PLANET. 

The  progress  of  cooling,  down  to  the  time  of  the  first 
incrustation,  would  be  promoted  by  a  convective  circula- 
tion between  the  central  and  peripheral  parts,  or,  in  case 
of  central  solidification,  between  the  solid  core  and  the 
periphery.  The  effect  would  be  to  equalize  the  tem- 
perature of  all  parts  of  the  planetary  mass.f  It  might 
be  supposed,  therefore,  that  at  the  epoch  of  first  incrusta- 
tion the  whole  temperature  would  be  but  little  above  the 
point  at  which  solidification  from  cooling  might  begin. 
Thus  the  maximum  temperature  of  the  heated  interior  of 
a  planet  might  be  conceived  to  be  about  that  at  which  the 
matter  of  the  planet  liquefies  under  the  atmospheric  pres- 
sure on  the  planet's  surface.  As  a  larger  planet  implies  both 
a  greater  mass  of  atmosphere  and  an  intenser  gravitating 

*  These  matters  will  be  more  particularly  discussed  in  treating  of  the  earth. 

•f  Sir  William  Thomson  has  shown  that  if  the  rate  of  increase  of  tempera- 
ture in  penetrating  the  earth  should  be  found  to  suffer  a  diminution  at  greater 
depths  than  have  been  as  yet  explored,  this  fact  would  imply  a  uniform  internal 
temperature  below  a  certain  depth  (Trans.  Oeo.  Soc.,  Glasgow,  vi,  45). 


222  A    COOLING    PLANET. 

power,  both  causes  would  increase  atmospheric  pressure, 
and  hence  lower  the  temperature  at  which  incrustation 
would  begin.  This  implies  that  the  central  portion  of  a 
large  p'lanet  is  less  hot,  and  must  consequently  require  a 
shorter  period  for  cooling,  aside  from  the  consequence  of  a 
greater  amount  of  heat  to  be  radiated.  Inferior  density 
would  operate  in  the  same  direction.  For  these  two 
reasons,  therefore,  the  larger  planet  should  not  linger  pro- 
portionately long  in  the  highly  heated  stages. 

§  6.     TIDAL  ACTION   AND   ITS  CONSEQUENCES  IN 
PLANETARY   HISTORY. 

I  believe  that  the  geologist  who  had  studied  all  the  text-books  in  exist- 
ence might  still  be  unacquainted  with  the  very  modern  researches  [on  palaeozoic 
high  tides]  which  I  am  attempting  to  set  forth.  Yet  it  seems  to  me  that  the 
geologists  must  quickly  take  heed  of  these  researches.  They  have  the  most 
startling  and  important  bearing  on  the  prevailing  creeds  in  geology.  One  of 
the  principal  creeds  they  absolutely  demolish.— Prof.  R.  8.  BALL:  Nature, 
Dec.  1,  1881. 

The  ebb  and  flow  of  the  tidal  wave,  therefore,  consists  not  only  in  an 
alternate  rising  and  falling  of  the  waters,  but  also  in  a  slow,  progressive 
motion  from  cast  to  west.  The  tidal  wave  produces  a  general  western  current 
in  the  ocean.— J.  R.  MAYER:  Celestial  Dynamics. 

1.  Some  Elementary  Principles. —  The  influences  of 
cosmical  tides  are  various,  important,  and  everywhere  felt. 
Tidal  movements  are  as  universal  as  gravitation  itself; 
and  late  researches  have  shown  that  cosmic  tides  have 
been  deeply  concerned  in  the  establishment  of  the  planet- 
ary relations  observed  in  our  system.  A  tide  may  be 
defined  as  the  prolateness  of  a  body  resulting  from  the 
attraction  of  another  body.  As  no  matter  is  known  to 
exist  which  is  absolutely  rigid  and  incompressible,  there 
can  be  no  state  of  solidity  so  absolute  as  to  be  exempt 
from  the  liability  to  tidal  deformation  under  the  gravita- 
tional power  of  cosmic  masses.  Between  absolute  solidity 
and  perfect  molecular  mobility  exist  all  grades  of  consist- 
ency, from  ordinary  solidity  through  the  various  degrees 


TIDAL   ACTION    IX    PLANETARY    HISTOEY.  223 

of  viscosity,  liquidity  and  gaseity.  These  various  condi- 
tions of  matter  are  themselves  relative  to  pressure,  tem- 
perature and  gravitation;  since,  at  a  given  pressure,  all 
substances  pass,  with  increase  of  temperature  to  the 
liquid  and  aeriform  conditions;  and  at  a  given  temperature, 
however  high  (within  certain  limits),  all  substances  pass, 
with  increase  of  pressure,  to  the  liquid  and  solid  condi- 
tions; and  at  given  pressure  and  temperature,  all  sub- 
stances tend  more  and  more,  under  increase  of  gravity,  to 
behave  like  liquids,  and  under  diminution  of  gravity,  to 
behave  like  gases.  Moreover,  there  is  no  solidity  so  com- 
plete that  in  the  presence  of  the  mighty  forces  of  nature, 
the  substance  does  not  yield  like  the  simplest  liquid.  In 
fact,  it  may  well  be  doubted  whether  the  attractions 
exerted  by  the  sun  and  planets  feel  to  a  very  important 
extent,  a  difference  in  the  resistances  offered  by  the  solid 
and  liquid  states  upon  the  bodies  subject  to  their  influ- 
ence. The  most  stubborn  granites,  diorites  and  quartzites 
may  probably  be  conceived  as  fluids  in  relation  to  all  the 
greater  cosmic  forces.* 

Tidal  results  depend  upon  the  unequal  influences 
exerted  by  an  attracting  body  upon  the  nearer  and  re- 
moter parts  of  the  body  influenced.  The  attraction 
exerted  by  one  body  upon  another  produces  the  same  total 
result  as  if  the  whole  force  were  applied  at  the  centre  of 
gravity.  But  meantime,  the  different  parts  of  the  affected 
body  will  be  set  in  motion  in  respect  to  each  other,  be- 
cause, being  at  different  distances  from  the  attracting 
body,  they  are  acted  on  with  different  intensities  of  force. 
The  parts  nearest  the  attracting  body  will  be  more  strongly 
influenced  than  the  more  central  parts,  and  will  conse- 
quently manifest  a  stronger  tendency  than  the  more  cen- 

*For  an  impressive  view  of  the  magnitude  of  such  forces,  see  an  article  by 
C.  B.  Warring,  in  Pop.  Sci.  Monthly,  xvii,  612-8,  Sep.,  1880,  and  a  similar  one  by 
E.  L.  Larkiu,  in  Kansas  City  Rev.  of  Sci.  and  Industry,  vii,  96-9,  June,  1883. 


224  A    COOLING    PLANET. 

tral  parts  toward  the  attracting-  body.  They  will  begin  to 
retire  from  the  more  central  parts,  and  will  actually  move 
away  from  them  until  restrained  by  the  cohesion  of  all  the 
parts  with  each  other,  and  by  the  tendency  of  all  masses 
of  matter  to  retain  the  spherical  form.  The  restraining 
influence  of  the  last-named  tendency  is  the  same  for  all 
states  of  matter  where  the  mass  is  the  same;  but  the 
restraining  influence  of  mutual  cohesion  of  parts  varies 
with  the  state  of  the  matter.  A  given  attraction  will 
therefore  produce  a  greater  tidal  result  in  an  aeriform 
or  liquid  body  than  in  one  which  is  viscid  or  nominally 
solid. 

But  further,  the  central  parts  of  a  body  influenced  by 
a  tidal  attraction  yield  more  than  the  remotest  parts. 
They  tend,  therefore,  to  leave  the  remotest  parts  behind, 
and  these  become  drawn  out  into  a  retral  prolongation 
until  restrained  and  held  down  by  mutual  cohesions  and 
the  law  of  sphericity.  We  have,  therefore,  a  tidal  protu- 
berance on  two  opposite  sides  of  the  body,  produced  sim- 
ultaneously. They  are  a  tide  and  an  anti-tide.  The  two 
tidal  curves  are  similar;  they  are  produced  by  the  same 
forces,  but  the  curve  of  the  anti-tide  is  reversed  in  respect 
to  the  curve  of  the  tide.  The  force  raising  it  is  a  deficient 
attraction;  it  is  virtually  a  force  acting  in  the  opposite 
direction  from  the  real  attraction.  In  short,  the  anti-tide 
may  be  conceived  as  produced  by  the  attraction  of  another 
body  situated  on  the  side  opposite  the  real  tide-producing 
body;  and  this  may  be  designated  the  anti-tide-producer. 

The  anti-tide,  however,  is  somewhat  less  than  the  tide. 
The  excess  of  attraction  producing  the  tide  is  greater  than 
the  deficiency  of  attraction  producing  the  anti-tide.  This 
would  not  be  the  case  if  the  attraction  diminished  simply 
with  increase  of  distance.  Attraction  diminishes  with 
increase  of  the  square  of  the  distance. 

There  are  three  conceivable  general  cases  under  which 


TIDAL   ACTION    IN    PLANETAKY   HISTORY.  225 

tidal  actions  may  be  exerted.*  (1.)  Where  the  tide-bear- 
ing body  is  homogeneous,  or  varying  in  density  toward 
the  centre  according  to  some  fixed  law.  Here  every 

*The  statements  made  in  the  present  connection  on  the  subject  of  tides, 
embrace  only  such  generalities  as  concern  the  main  course  of  planetary  evolu- 
tion. Any  particular  case,  like  the  oceanic  tides  on  the  earth,  may  involve 
numerous  considerations  of  which  no  account  is  necessary  here  —  such  as 
variations  in  distance  of  tide-producer;  changes  in  declination  in  reference  to 
equator  of  tide-bearer;  interferences  of  tidal  actions  of  two  or  more  tide- 
producers;  consequences  of  different  rates  of  change  of  right  ascension  of 
different  tide-producers;  the  absolute  angular  velocity  of  the  tide-producer  in 
its  orbit;  rotation  and  oblateness  of  tide-bearer;  depth  and  variations  in  depth 
of  enveloping  film ;  relative  density  of  film,  its  actual  index  of  viscosity,  its 
actual  density  and  its  friction  against  resistances.  In  our  general  view  it 
will  only  be  necessary  to  regard  the  relative  tidal  efficiency  of  the  tide-pro- 
ducer, the  relative  mass  and  volume  (radius  and  density)  of  the  tide-bearer, 
and  the  general  fact  of  axial  and  orbital  movements. 

Xo  theory  of  tides  has  been  mathematically  worked  out,  which  answers  all 
the  requirements  of  tidal  phenomena  in  the  terrestrial  waters.  The  funda- 
mental conceptions  embodied  in  the  "Equilibrium  Theory"  of  Newton  and 
Daniel  Bernoulli  are  undoubtedly  correct;  but  this  theory  neglects  many  modi- 
fying conditions  in  the  actual  case,  and  therefore  fails  in  many  particulars. 
But  it  is  not  just  to  pronounce  it  "contemptible,"  as  Sir  G.  B.  Airy  has  done. 
.The  "Dynamical  Theory"  of  Laplace,  generally  considered  more  rational, 
though  also  severely  criticised,  conceives  each  particle  of  the  water  in  motion, 
and  investigates  the  forces  acting  on  it.  The  tidal  swell  results  from  the  flow  of 
water  on  both  sides  toward  it.  and  the  ebb  results  from  the  flow  in  both  directions 
away  from  it.  The  working  out  of  the  theory,  however,  has  to  assume,  con- 
trary to  the  facts,  that  the  earth  is  completely  covered  with  water,  and  that  it  is 
of  uniform  depth  throughout  any  parallel  of  latitude.  The  "Wave  Theory," 
expounded  by  Sir  G.  B.  Airy,  is  based  on  the  laws  of  movement  of  waves  along 
canals  relatively  shallow  and  narrow,  and  applies  especially  to  the  motion  of 
tidal  waters  in  shallows,  estuaries  and  rivers,  where  the  other  theories  fail; 
but  for  the  phenomena  of  the  open  sea,  it  makes  the  false  assumption  that  the 
wave  is  restricted  to  narrow  canals,  instead  of  spreading  freely  in  all  direc- 
tions. For  our  present  use,  the  conceptions  of  the  Equilibrium  Theory  are 
entirely  adequate. 

The  completes!  general  exposition  of  tidal  theories  may  be  found  in  Airy's 
article  on  Tides  and  Waves,  in  Encyclopaedia  Metropolitana,  vol.  v,  pp.  241*- 
396*.  For  the  purposes  of  the  general  student,  however,  a  much  more  satis- 
factory general  exposition  may  be  found  in  the  Appendix  to  Johnson's  Cyclo- 
pcedia,  by  Gen.  J.  G.  Barnard.  See  also,  Prof.  Wm.  Ferrel's  Tidal  Researches, 
Appendix  to  U.  S.  Coast  Survey,  1874,  or  thereabouts.  See  also,  as  collateral, 
Ferrel's  papers  on  the  Motions  of  Fluids  and  Solids  Relative  to  the  Earth's  Sur- 
face, in  eight  communications  to  the  Mathematical  Monthly,  Cambridge,  Mass., 
1859-60,  vols.  i  and  ii ;  also,  his  Methods  and  Results  of  Meteorological  Researches, 
for  the  Use  of  the  Coast  Pilot,  Part  I,  1877,  Part  II,  1880  (on  Cyclones,  Water- 
spouts and  Tornadoes). 
15 


A   COOLING    PLANET. 


PIG.  38.  — COMPOUND  TIDE. 

a »«,  tidal  elevation  iu  less  viscous 
envelope. 

o  c,  tidal  depression  in  less  vis- 
cous envelope. 

1 1,  tidal  elevation  in  morp  viscous 
nucleus. 

r  g,  tidal  depression  in  more  vis- 
cous nucleus. 

mt,  depth  of  envelope  at  mean 
tide. 

at,  depth  of  envelope  at  high  tide 
over  nucleus  supposed  rigid. 

a  e,  depth  of  envelope  at  high  tide 
overyieldingnucli  »s—at-<(. 

cr,  depth  of  envelope  at  low  tide 
over  nucleus  supposed  rigid 

c  g,  depth  of  envelope  at  low  tide 
over  yielding  nucleus  =  cr-\- 
rg. 


successive  layer  undergoes  tidal 
disturbance  according  to  its  dis- 
tance from  the  centre.  The 
whole  body  is,  therefore,  sym- 
metrically transformed,  and  be- 
comes a  prolate  spheroid,  with 
a  prolate  axis  a  b,  Figure  37, 
varying  inversely  as  the  coeffi- 
cient of  viscosity.  This  we  will 
designate  a  deformative  tide. 
Here  m  o  np  is  a  section  of 
the  undisturbed  sphere,  and 
a  c  b  d  a  section  of  the  body 
when  rendered  tidally  prolate. 
The  tidal  elevation  is  expressed 
by  a  in  and  the  depression  by 
o  c.  (2.)  Where  the  tide-bear- 
ing body  consists  of  a  cen- 
tral part,  rtsu,  Figure  38, 
having  a  higher  coefficient  of 
viscosity  than  the  surrounding 
part.  Here  the  nucleus  will 
yield  in  a  less  ratio  than  the 
envelope.  The  prolateness  of 
the  envelope,  but  for  the  influ- 
ence of  relative  rotation,  will 
be  the  same  as  if  the  whole 
body  were  of  the  same  sub- 
stance as  the  envelope,  and  the 
prolateness  of  the  nucleus  will 
be  nearly  the  same  as  if  the 
envelope  were  absent.  The 
tidal  fluctuations  in  the  en- 
velope are  expressed  as  in  the 
deformative  tide;  but  the  re- 


TIDAL   ACTION    IN    PLANETARY    HISTORY. 


suiting   depth   of    the   envelope  over  the   tidally   raised 
nucleus,  will  be  the  depth  resulting  in  case  of  a  rigid 
nucleus,  diminished  by  the  amount  of  the  actual  tide  in 
the.  viscid  nucleus.     (3.)   Where   the   tide-bearing   body 
consists  of  a  perfectly  rigid  nucleus,  rtsu,  Figure  39, 
and  an  envelope  susceptible  to  tidal  action.     Here,  also, 
the  prolateness,  disregarding  rotation,  becomes  the  same 
as  if  the  whole  body  were  of 
the  matter  forming  the  envel- 
ope.    The    dimensions   of    the 
tide  in  the  envelope  will  be  ex- 
pressed as  before;  but  the  total 
depth,  a  t,  of  the  envelope  at 
high  tide,  will  not  be  diminished 
by  any  tide  in  the  nucleus;  nor 
will  its  depth,  c  r,  at  low  tide, 
be  increased  by  any  ebb  in  the 
nucleus.     Though  it  is  doubtful 
whether  this  case  exists  in  na- 
ture, we  have  to  deal  with  cases 

where  the  nucleus  is  more  or  less  rigid,  and  the  degree  of 
rigidity  is  indicated  by  the  difference  between  a  e,  Figure 
38,  the  actually  measured  depth,  and  a  t,  the  depth  calcu- 
lated on  the  hypothesis  of  a  perfectly  rigid  nucleus.  This 
difference  shows  the  amount  of  tidal  yielding  in  the  nu- 
cleus. But  even  this  operation,  however  desiderated,  has 
not  been  satisfactorily  accomplished  in  practice. 

The  total  vertical  fluctuation  of  the  tide  is  the  sum  of 
the  flood  and  ebb  tides;  or  in  Figure  38,  it  is  am  +  o  c. 
The  flood  tide  rises  twice  as  high  above  the  mean  sphere 
as  the  ebb  tide  falls  below  it.  This  is  apparent  from  the 
general  consideration  that  the  deficiency  of  fluid  causing 
the  ebb  is  spread  over  a  greater  surface  than  the  excess  of 
fluid  causing  the  two  flood-tides.  The  one  is  spread  over 
a  broad  zone  encircling  the  ellipsoid,  while  each  flood-tide 


FIG.  39.  — FILM  TIDE. 


A    COOLING    PLANET. 


is  spread  over  a  circular  area  of  about  one-fourth  the 
extent.  Each  circular  area,  nevertheless,  is  more  than  a 
quadrant  in  breadth,  having  a  radius,  in  a  homogeneous 
spheroid,  of  54°  44'. 

The  tidal  effect  on  the  same  tide-bearer,  is  directly  as 
the  mass  of  the  tide-producer,  and  inversely  as  the  cube  of 
its  distance.  But  for  any  other  tide-bearer,  the  effect  is 
also  proportional  to  its  radius.* 

*  These  principles  result  from  the  following  reasoning: 
C 


FIG.  -JO. — QUANTITATIVE  RELATIONS  OF  TIDES. 


Let  D  =  E  M  (Figure  40)=  distance  between  centres  of  tide-bearer  and  tide 
producer, 

m  =  mass  of  tide-producer, 

R  =  E  B  =  radius  of  tide-bearer. 

Then  the  attractions  at  B,  E  and  A  are  expressed  by 


Subtracting  the  second  from  the  first,  and  the  third  from  the  second,  we 
get,  very  nearly, 

p,     =  Excess  of  attraction  at  B  over  E ; 

— j—  =  Excess  of  attraction  at  E  over  A. 

But  ttie  latter  is  actually  a  little  less  than  the  former. 

These  expressions  show  that  the  efficiency  of  the  tidal  force  of  the  same  tide- 
producer  vurlts  directly  as  the  radius  of  (he  tide-bearer  and  inversely  as  t/ie  cube 
of  the  distance  of  the  tide-producer. 

Now,  further,  if  we  assume  any  point  P,  on  the  surface  of  the  tide-bearer, 
at  the  angular  distance  <fr  from  the  line  E  M,  joining  the  centres,  and  put  g  for  in- 
tensity of  gravity  on  tide-bearer,  and  p  for  the  relative  density  of  a  thin  external 
film  covering  a  rigid  nucleus,  then  the  elevation  (or  depression)  of  P  above  the 
surface  of  the  equivalent  sphere,  expressed  in  terms  of  radius  (assumed  as 
unit*,  will  be 


TIDAL   ACTION   IN    PLANETARY   HISTORY.  229 

There  is  another  cause  of  tidal  protuberances  in  certain 
cases.  Suppose  two  bodies  in  space  having  equal  masses 
and  densities  revolve  about  the  common  centre  of  gravity 
between  them.  Now,  each  is  in  a  position  to  create  tidal 
effects  on  the  other  through  the  operation  of  gravitation, 
as  just  explained.  But,  in  addition  to  this,  the  differential 

This  is  a  general  expression  for  the  height  of  any  point  of  a  film-tide  having 
the  relative  density  p  (that  of  the  nucleus  being  unity). 
If  the  spheroid  is  homogeneous,  that  is,  if  p  =  1, 

T=2-w^f(cos2*-i)-    -  -  -  "» 

If,  in  the  homogeneous  spheroid  we  take  <}>  =  0°  or  180°,  then  cos  2  <£  —  -^  =  f , 
and 

T'=  I  -j^-  =  height  of  flood  -tide, (3) 

If  we  take  <f>  =  90°  or  270°,  then  cos  2  <£  -  ^  =  -  £,  and 

T"  =  -  £  .  ^-  =  depression  of  ebb  tide.    -  -    (4) 

It  may  be  added  here  that,  in  the  case  of  the  earth,  p  =  -f^,  and  using  this 
value, 

T'=ff.j^-  =  theoretical  mean  flood-tide. (5) 

while  T"  =-  ff  'ij-f-  =  theoretical  mean  ebb-tide.    -  -    (6) 

To  find  at  what  angular  distance  from  the  zenith  of  the  tide-producer  the 
tide  in  a  homogeneous  spheroid  is  0,  we  have  the  equation, 


in  which  as  <t>  is  the  only  variable  quantity  we  must  have  cos  2  <f>  =  |,  or  cos  <£  = 
fT=  .57735  =  cos  54°  44'.  This  arc  then,  is  the  radius  of  the  spherical  menis- 
cus formed  by  the  flood-tide  or  tidal  protuberance. 

To  render  the  formula  (1)  more  general,  we  must  introduce  the  radius  of  the 
tide-bearer  as  a  factor,  and  this  gives 
3m  R        1 


If,  in  any  other  couple  tidally  connected,  the  quantities  D,  R.  m,  g  have  the 
values  d,  r,  n,  g',  the  height  of  the  tide  will  be 

t-^JLL.    —l—(    s2d_  n 
~~  2 dig'  'l-sp(co  tn 

whence  -^  =  —  •  -^  •  -^  .  iL.    But  if  M  and  M'  be  the  masses  of  the  two  tide- 
bearers  in  these  values  of  T  and  t,  then  g'  =  g  ^ •—•>  a:i«l  substituting, 

D3    R2      M      n 
T  '  W~ri  "Win' 

This  gives  the  height  of  the  tide  on  one  spheroid  with  one  tide-producer  in 
terms  of  the  height  of  the  tide  on  another  spheroid  with  another  tide-producer. 


230  A   COOLING   PLANET. 

centrifugal  tendency  on  the  nearer  and  farther  sides  of 
each  in  respect  to  the  common  centre  of  gravity,  will  im- 
part to  the  farther  side  a  tendency  to  recede  from  the 
centre,  and  to  the  centre  a  tendency  to  recede  from  the 
nearer  side.  The  result  must  be  the  same  as  when  similar 
tendencies  are  produced  by  gravity.  The  body  becomes  a 
prolate  spheroid.  This  prolateness  becomes  important 
where  a  body  of  considerable  volume  revolves  with  ra- 
pidity in  an  orbit  comparatively  small,  as  when  a  body  of 
small  mass  and  low  density  revolves  rapidly  about  another 
of  large  mass.  But  in  a  couple  like  the  earth  and  moon 
where  the  centre  of  gravity  lies  so  near  the  centre  of  the 
larger  body,*  this  cause  would  hardly  produce  a  percepti- 
ble prolateness  of  the  larger  body.  In  aeriform  masses  of 
matter,  however,  where  the  volume  is  generally  great,  and 
cohesion  of  parts  a  minimum,  we  might  expect  this  cause  to 
become  quite  preceptibly  operative.  A  tidal  deformation 
produced  by  this  cause  alone  would  tend  to  transfer  the 
heavier  parts  of  the  bod}'  to  the  remoter  side,  and  leave  the 
lighter  upon  the  nearer  side.  But  this  action  could  only 
coexist  with  proper  tidal  action,  which  alone  would  create 
a  tendency  in  the  heavier  parts  to  pass  to  the  nearer  side, 
leaving  the  lighter  to  occupy  the  remoter  side.  The  cir- 
cumstances under  which  one  of  these  tendencies  would 
prevail  over  the  other  in  a  body  (like  our  moon)  turning 
always  the  same  side  toward  the  tide-raising  body  (like 
the  earth)  have  been  heretofore  discussed.  [Part  I,  Chap, 
ii,  §  4,  3,  (2).]  If  the  rotary  and  orbital  motions  are  not 
synchronous,  the  effect  of  tidal  action  upon  the  distribu- 
tion of  heavier  and  lighter  parts  must  be  nullified. 

2.  General  Effects  of  Tidal  Action  in  Planetary  Life. 
Heretofore  in  discussing  the  vicissitudes  of  nebular  masses 
disengaged  from  primitive  nebul;p  by  a  process  of  annula- 

*The  centre  of  gravity  between  the  earth  and  moon  Is  only  2,963  miles 
from  the  earth's  centre.  •  "• 


TIDAL   ACTION    IN    PLANETARY    HISTORY.  231 

tion,  I  have  had  occasion  to  direct  attention,  in  a  general 
way,  to  the  effects  of  tidal  action  both  as  resulting  di- 
rectly from  attractions  and  also  from  differential  centrifu- 
gal tendencies.  In  the  early  history  of  planetary  bodies 
tidal  actions  acquire  a  remarkable  degree  of  importance. 
I  desire,  therefore,  in  entering  on  a  recital  of  the  events 
of  primitive  planetary  history,  to  explain  preliminarily, 
the  general  mode  of  reaction  of  tidal  masses.  I  refer  here 
to  actions  resulting  from  the  existence  of  tides. 

I  have  stated  that  all  bodies  are  susceptible  of  some 
degree  of  tidal  deformation.  The  character  of  the  tidal 
effect  depends,  under  a  given  tidal  action,  on  the  facility 
with  which  the  parts  tidally  moved  change  their  relative 
positions,  and,  upon  a  rotating  spheroid,  the  promptness 
with  which  they  respond  to  the  tidal  solicitation.  These 
conditions  concern  the  height  of  the  tide  and  its  position 
in  reference  to  the  tide-producing  body.  In  a  perfect 
fluid  the  height  of  the  tide  will  be  determined  only  by  the 
general  law  of  sphericity;  and  the  apex  of  the  tide  will  be 
on  the  shortest  line  joining  the  centres  of  gravity  of  the 
two  bodies.  In  matter  possessed  of  any  degree  of  vis- 
cosity, the  height  of  the  tide  will  be  less  than  in  a  perfect 
fluid,  and  the  position  of  the  tide  will  be  somewhat  ahead 
of  the  zenith  position  of  the  tide-producing  body  Viewed 
in  reference  to  time  of  culmination  of  the  tide-producer, 
the  tide  therefore  lags  behind.  In  a  system,  like  our  solar 
system,  where  the  prevailing  motions  are  from  west  to 
east,  the  crest  of  the  tide  will  be  to  the  east  of  the  zenith 
position  of  the  tide-producing  body.  In  other  words,  to 
an  observer  at  the  apex  of  the  tide,  the  tide-producing 
body  will  have  passed  the  zenith.  Thus,  if  O  and  C  be  the 
centres  of  the  two  bodies  concerned,  and  the  body  O  is 
rotating  in  the  direction  of  the  arrow,  then  the  apex  of 
the  tide,  B,  will  have  passed  the  point  A,  under  the  zenith 
of  the  tide-producing  body  C,  and  will  be  to  the  east  of 


A    COOLING    PLANET. 


FIG.  41. — ILLUSTRATING  A  LAGGING  TIDE. 

A  by  the  angular  distance  BOA.  This  circumstance, 
due  to  the  viscosity  of  the  body  O,  gives  rise  to  some  very 
interesting  deductions.  These  I  will  now  endeavor  to 
make  plain. 

(1.)  The  lagging  of  the  tide  tends  to  a  retardation  of 
the  rotary  motion  of  the  tide-hearing  body. — A  simple 
inspection  of  the  figure  suffices  to  show  that  the  attrac- 
tion of  C  upon  the  tidal  protuberance  at  B  must  tend  to 
draw  B  around  toward  A.  It  is  true  that  attraction  is 
exerted  similarly  by  C  upon  the  tidal  protuberance  at  D; 
but  the  influence  exerted  upon  the  centre  is  greater,  and 
the  effect  of  this  is  a  relative  movement  of  D  backward. 
To  make  this  plainer  we  may  conceive  the  anti-tide  caused 
by  an  attraction  from  the  opposite  direction,  C'O;  then  it 
is  evident  that  the  tangential  component  of  this  attrac- 
tion, exerted  at  D,  will  tend  to  rotate  the  spheroid  in  a 
direction  contrary  to  the  arrow.  But  as  B  and  D  are  con- 
strained to  the  surface  of  the  spheroid,  the  tendency  of 
those  two  points  is  to  bring  the  prolate  axis  BD  into 
coincidence  with  the  line  C'C,  passing  through  the  centres 
of  gravity  of  the  tide -bearer  and  tide-producer,  that  is, 
the  lagging  of  the  tide  results  in  a  force  which  opposes 
the  rotation  of  the  body  O.* 

*  The  horizontal  component  of  the  attraction  which  tends  to  move  B  toward 
A  may  be  represented  by  the  tangent  B  E ,  Figure  41.  Then  by  the  principle  of 
the  parallelogram  of  forces  we  may  readily  d«dnce  a  rough  general  expression 


TIDAL   ACTION    IN    PLANETARY   HISTORY.  233 

This  cause  of  retardation  must  be  set  down  as  real,  and 
in  the  actual  constitution  of  matter,  as  universal  as  the 
existence  of  tides.  But  now  the  viscosity  of  matter  comes 
into  action  in  another  way.  The  tide-bearer  not  being 
rigid,  the  retarding  effect  is  not  fully  experienced.  The 
protuberant  mass  at  B  tends  to  slide  over  the  bodily 
mass,  and  to  undergo  a  translation  toward  A.  The 
amount  of  actual  translation  will  be  inversely  as  the 
coefficient  of  viscosity.  In  a  highly  viscous  mass  the 
motion  of  translation  will  be  but  slight,  and  the  protuber- 
ance will  yield  only  as  it  can  draw  the  whole  body  around 
with  it,  or  a  little  more  than  this.  In  a  highly  fluid  mass 
the  protuberance  will  yield  more  readily,  the  translatory 
movement  will  be  greater  for  the  same  lagging,  but,  on 
the  other  hand,  the  lagging  will  be  less,  and  the  horizontal 
component  of  the  tidal  force  will  be  diminished  also. 

In  the  case  where  the  tide-bearer  is  internally  more 
rigid  than  near  the  surface,  or  has  parts  more  rigid, 
against  which  the  translated  tidal  swell  may  strike,  the 
retarding  influence  assumes  more  characteristically  the 
nature  of  frictional  action.  This  action  must  exist  when- 
ever any  of  the  moving  parts  yield  more  readily  than 
other  parts  in  juxtaposition  with  them.  Retardation 
through  frictional  action  presents  the  most  intelligible 

for  this  component.  For,  in  all  cases  where  the  angle  B  O  A=a  is  small,  the 
distance  AE  is  relatively  inconsiderable,  and  CE  may  be  taken  as  the  distance 
of  the  tide-producer  from  the  surface  of  the  tide-bearer,  and  O  B  may  be  taken 
as  the  mean  radius  of  the  latter.  Then,  if  0=B  C  E,  the  angle  at  the  tide-pro- 
ducer subtended  by  the  tangent  B  E,  we  shall  have  in  the  triangle  B  O  C, 

sin  0=sin  a  |£. 
Also,  in  the  triangle  C  B  E, 

B  E  :  B  C ::  sin  6:  sin  B  E  C=sin  (90°  +  a)=cos  «, 

...BMO^f. 

COS  o 

In  this  expression  B  C  represents  the  whole  attraction  upon  B,  and  B  E,  its 
horizontal  component,  or  the  value  of  the  force  acting  against  the  rotation  of 
the  tide-producer.  Putting  F  for  the  former  and  substituting  the  value  of  siii  6. 


234  A   COOLING   PLANET. 

case  where  a  film  like  the  ocean  covers  a  nucleus  rela- 
tively solid  which  rises  above  the  surface  of  the  film  in 
certain  regions,  presenting  shallows  and  fixed  resistances 
to  the  tidal  movements  of  the  film.  The  mere  vertical 
rise  and  fall  of  the  tides  will,  in  such  case,  establish  cur- 
rents, the  initial  impulse  of  which  is  toward  the  crest  of 
the  tide  from  both  directions,  but  which,  from  the  config- 
uration of  the  solid  resistances,  may  be  deflected  in  any 
assignable  direction.  While  these  currents  must  exert 
important  erosive  agency,  it  is  not  these  which  develop 
the  friction  that  tends  to  retard  the  rotation  of  the  tide- 
bearer.  These  currents  may,  indeed,  act  in  all  directions. 
It  is  the  translatory  movement  of  the  tide  which  deter- 
mines a  balance  of  action  in  the  direction  of  the  transla- 
tion; that  is,  in  our  system,  toward  the  west.  Thus,  the 
eastern  borders  of  the  resistances  should  receive  somewhat 
severer  action  than  the  western.  While,  however,  all  these 
actions  and  movements  are  real,  they  are  very  minute,  and 
can  only  become  of  cosmical  importance  when  their  results 
accumulate  through  secular  periods. 

In  consequence  of  the  retral  translation  of  the  tidal 
mass,  its  position  will  not  be  accurately  at  B,  the  point 
determined  by  the  viscosity  of  the  tide-bearer,  but  at 
some  point  between  B  and  A.  The  actual  tide  will  occur, 
therefore,  a  little  sooner  than  might  be  calculated  on  the 
basis  of  viscosity  alone.  There  ought  to  be  thus  a  slight 
anticipation  of  the  tide. 

One  point  more.  The  apex  of  the  tidal  swell,  but  for 
the  lagging  here  under  consideration,  would  be  exactly 
beneath  the  tide-producer.  But.  in  consequence  of  the 
lagging,  the  tidal  apex  is  developed  some  distance  to  the 
east  of  the  zenith.  The  point  which  had  been  beneath 
the  zenith  has  been  carried  around  by  the  rotation  of  the 
tide-bearer.  It  has  been  carried  around  on  the  equator  or 
a  parallel  of  latitude.  For  the  present  explanation  let  us 


TIDAL  ACTIOJ?   IN"   PLANETARY   HISTORY.  235 

suppose  the  tidal  crest  to  lie  under  the  equator.  The 
tide  producer  acts  upon  the  protuberant  mass  from  a  posi- 
tion a  little  further  west.  There  are  two  reasons  now 
why  the  greatest  translatory  effect  should  be  produced  at 
the  apex  on  the  equator,  first,  that  part  of  the  tidal 
swell  is  nearer  the  tide-producing  body;  second,  the  apex 
being  more  elevated  than  the  portions  lying  to  the  north 
and  south,  must  be  more  susceptible  to  the  attraction 
exerted  upon  it.  The  tidal  action  is  more  transverse,  and 
the  horizontal  component  is  greater.  The  consequence  is 
that  the  apical  portion  of  the  tidal  swell  must  recede 
westward  more  than  the  portions  to  the  north  and  south. 
If,  therefore,  the  meridian  passing  over  the  apex  of  the 
tidal  swell  at  any  moment  could  be  fixed  to  the  receding 
surface,  it  would  be  broken  at  the  equator  into  two  curves 
inclined  to  the  meridian,  and  presenting  their  convexities 
toward  the  east.  The  equatorial  portion  would  be  borne 
westward  more  than  the  other  portions.  This  curious  and 
interesting  result,  first  made  known  by  Mr.  G.  H.  Darwin, 
will  be  hereafter  applied  to  the  case  of  the  earth. 

In  Figure  42  I  have  attempted  to  illustrate  more  fully 
the  consequences  of  a  lagging  tide,  as  far  as  explained, 
and  also  other  consequences  remaining  to  be  noticed. 
Here  we  have  a  perspective  view  of  a  planetary  spheroid 
or  tide-bearer,  having  its  axis  N  S  inclined  to  the  plane  of 
the  orbit  O  M,  in  which  is  moving  a  moon  or  tide-producer. 
The  direction  of  the  axial  and  orbital  movements  is  shown 
by  the  arrows.  The  broken  and  dotted  lines  in  the  view 
of  the  planet  represent  parts  on  the  invisible  hemisphere. 
N  S  is  the  axis  of  rotation;  E  E  E  E  is  the  equator;  L  L  L  L 
is  the  great  circle  of  intersection  of  the  plane  of  the  orbit 
O  M  with  the  surface  of  the  planet.  It  outs  the  equator 
at  two  opposite  points,  X,  X.  C  C  C  C  is  a  parallel  or 
small  circle  tangent  to  the  last  mentioned  at  m.  Other 
•small  circles  are  drawn,  and  also  several  meridians,  for  the 


A    COOLING    PLANET. 


FIGURE  42.— ILLUSTRATING  THE  SKCLI.AI:  EFFECTS  or  TIDES  IN  A 

ROTATING  Viscous  SPHEROID. 
N  and  S  are  the  poles  of  the  spheroid. 
£  E  E  E,  the  equator. 
C  CC  C,  a  small  circle,  in  north  latitude,  parallel  with  the  equator  and  tangent  to 

L  L  L  L  at  m. 
P  P  P  P,  a  small  circle,  in  south  latitude,  parallel  with  the  equator  and  tangent  to 

L  L  L  L  at  m'. 


TIDAL   ACTION    IN    PLANETARY   HISTORY.  237 

purpose  of  giving  intelligibility  to  the  diagram.  We  are 
under  the  necessity  of  placing  the  tide-producer  M,  dis- 
proportionately near  the  tide-bearer;  but  this  only  exag- 
gerates the  quantities  which  it  is  desired  to  bring  into 
notice,  and  hence  is  a  real  help. 

No%v  the  tide-producer  is  supposed  to  be  in  the  zenith 
over  m,  and  accordingly  a  tidal  effect  is  progressing  at  m. 
But  this  effect,  in  consequence  of  viscosity,  does  not  reach 
its  culmination  until  the  rotation  of  the  planet  has  trans- 
ferred the  point  m  to  t,  and  t,  therefore,  is  the  place  <?f 
high  tide.  Suppose  M  to  be  the  tide-producing  body  at 
this  juncture.  Then  a  tidal  protuberance  exists  on  the 
meridian  passing  through  t,  somewhat  to  the  east  of  the 
zenith  position  of  M,  and  the  attraction  of  M  exerted  upon 
t  tends  to  rotate  the  planet  backward,  around  the  axis  N  S, 
toward  m.  The  amount  of  this  tendency  is  the  retarding 
effect  of  the  lagging  tide.  The  apex  of  the  anti-tide  is  at 
t'  instead  of  m' ,  and  the  lagging  of  the  anti-tide  brings  it 
to  a  position  where  the  attraction  of  the  theoretical  anti- 
tide-producer  tends  to  draw  it  retrally  from  t'  toward  m', 
and  thus  as  before,  to  retard  the  rotational  motion  of  the 
planet. 

The  attraction  of  the  tide-producer  exerted  upon  t  pro- 
duces a  virtual  retral  motion  which  we  may  assume  repre- 
sented by  ttl.  The  distanced  £15  is  therefore  the  anticipation 

L  L  L  L,  intersection  with  the  spheroid's  surface  of  the  plane  of  the  orbit  of  the 

tide-producer. 

XX.  diameter  joining  intersections  of  equator  and  LLLL.     , 
M,  tide-producer,  assumed  to  be  vertically  overm. 
O  M,  portion  of  the  orbit  of  the  tide-producer. 

m,  point  under  M,  and  the  apex  of  the  tide  in  case  of  perfect  fluidity. 
t.  apex  of  the  tide  as  determined  by  lagging  from  m  to  I. 
1 1,  actual  apex  of  the  tide,  as  resulting  from  lagging  and  from  retral  slipping  from 

tiotl. 

m',t',li\  corresponding  points  of  the  anti-tide. 
Mr,  acceleration  of  the  tide-producer  caused  by  the  attraction  of  the  tide  from 

t,  or  more  exactly  from  1 1 . 
M'r,  recession  of  the  tide-producer  caused  by  its  acceleration  and  increased 

centrifugal  tendency. 


238  '  A    COOLING    PLANET. 

of  the  tide,  or  the  amount  by  which  it  occurs  sooner  than 
might  be  expected  when  the  calculation  of  its  position  is 
based  simply  on  the  amount  of  lagging  due  to  the  viscosity. 
It  will  be  borne  in  mind  that  the  retral  pull  may  be  con- 
ceived as  developing  in  part  an  actual  retardation  of  the 
planetary  spheroid,  and  in  part  a  retral  translation  of  a 
portion  of  the  more  fluid  film  upon  the  surface.  The  rela- 
tive amounts  of  retardation  of  the  whole  body,  and  retar- 
dation or  retral  translation  of  the  surface,  will  be  deter- 
mined by  the  viscosity  of  the  film  and  its  opportunities 
for  action  against  fixed  or  relatively  fixed  parts  of  the 
included  nucleus. 

Supposing  a  film  more  fluid  than  the  nucleus,  and  a  tide- 
producer  M,  acting  on  a  tidal  swell  whose  crest  is  at  t, 
then  obviously,  the  greatest  amount  of  retral  movement 
will  be  produced  at  t,  while  north  and  south  of  t  the  retral 
movement  will  be  less,  both  because  of  the  greater  dis- 
tance of  the  attracting  body  and  of  the  less  height  of  the 
tide. 

As  the  tide-producer  moves  in  its  orbit  it  reaches  a 
point  directly  over  the  node  X.  In  this  position  the  re- 
tarding factor  of  the  attraction  is  more  effective  than 
before,  and  the  linear  retral  motion  of  the  surface-film  will 
be  greater,  since  the  retarding  force  is  applied  at  a  greater 
distance  from  the  axis.  When,  at  a  subsequent  epoch, 
the  tide-producer  is  over  m' ,  and  the  tide  is  at  t' ,  then  the 
retarding  and  translatory  effects  become  precisely  as  at  m 
and  t.  Henc«  the  retarding  and  translatory  effects  attain 
a  maximum  when  the  tide-producer  is  nearly  over  the 
planetary  equator,  and  diminish  thence  during  the  northern 
and  southern  declinations.  That  is  to  say,  considering  the 
aggregate  translatory  effects  during  an  orbital  revolution 
of  the  tide-producer,  the  retral  movement  will  be  greatest 
at  the  equator  and  will  diminish  thence  toward  the  poles. 
The  equatorial  reg'ions  will  suffer  a  greater  westward  shift- 


TIDAL   ACTION    IN    PLANETAKY    HISTOBY.  239 

ing  of  longitude  than  regions  farther  north  and  south;  so 
that  lines  once  meridional  will  eventually  present  an  in- 
clined double  convexity  eastward,  with  north-eastward 
trends  north  of  the  equator,  and  south-eastward  trends 
south  of  the  equator. 

As  the  lagging  of  the  tide  results  from  the  viscosity  of 
the  tidally  disturbed  matter,  the  amount  of  the  lagging 
becomes  a  measure  of  the  viscosity.  But,  that  it  may  be 
accurately  such  measure,  correction  must  be  made  for  the 
retral  slipping  of  the  superficial  film  in  the  latitude  where 
the  apex  of  the  tide  is  situated. 

In  the  case  of  a  tide-bearer  constituted  of  a  nucleus  of 
higher  viscosity,  and  an  enveloping  film  of  lower,  each 
part  will  develop  its  own  tidal  protuberance,  and  that  of 
the  nucleus  will  lag  more  than  that  of  the  film.  This  is 
shown  in  the  adjacent  figure,  where  A  B  is  the  prolate 


FIG.  43.— DISCORDANT  TIDES  OF  NUCLEUS  AND  FILM. 

axis  of  the  film,  and  C  D  the  prolate  axis  of  the  nucleus. 
It  is  to  be  remarked,  in  view  of  this  state  of  things,  that 
the  problem  of  the  rigidity  of  the  nucleus  as  depending  on 
the  measured  depth  of  the  tide  A  a,  must  take  account  of 
the  fact  that  a  is  not  the  point  at  which  the  nuclear  tide  is 
developed. 

(2.)  The  lagging  of  the  tide  produces  a  sloio  reces- 
sion of  the  tide-producing  body. — Recurring  to  Figure  41, 
let  H  I  represent  a  portion  of  the  orbit  of  a  tide-producer 


240  A    COOLING    PLANET. 

moving  in  the  direction  of  the  arrow.  This,  according  to 
the  process  of  world-making  which  we  here  maintain,  will 
be  in  the  same  direction  as  the  rotation  of  the  tide-bearer. 
The  apex  of  the  tide  will  be,  therefore,  at  B,  in  advance 
of  the  position  of  the  tide-producer,  and  an  attraction  will 
be  exerted  by  the  tidal  mass  upon  C,  in  the  direction  C  B. 
While  the  greater  part  of  this  attraction  coincides  with 
the  mean  centripetal  force  drawing  C  toward  O,  a  small 
component  of  it,  as  the  diagram  shows,  tends  to  accelerate 
the  motion  of  C  in  the  direction  C  I.  But  C  was  supposed 
to  be  moving  with  such  orbital  velocity  as  held  it  balanced 
between  centripetal  and  centrifugal  forces,  and  if  now  that 
velocity  is  increased,  the  centrifugal  tendency  is  increased, 
and  C  tends  to  move  in  the  direction  of  the  tangent  C  G. 
That  is,  its  distance  from  O  is  increased.  But  now,  re- 
moved to  a  greater  distance,  the  centripetal  force  is  dimin- 
ished, and  the  tide-producer  moves  in  such  an  orbit  that 
its  diminished  centrifugal  tendency  again  equilibrates  the 
centripetal  tendency.  Thus  there  results  the  apparent 
anomaly  that  an  acceleration  of  the  body  in  its  orbit  leads 
to  retardation.  To  put  the  matter  in  another  light,  let  us 
consider  that  while  the  total  attraction  of  the  body  O  is 
the  same  with  or  without  the  tide,  one  part  of  it  when  the 
tide  exists,  is  exerted  in  the  direction  C  B  instead  of  C  O, 
and  develops  the  tangential  tendency  CG;  while  the  re- 
maining part  exerted  in  the  direction  C  O  is  less  than  the 
centripetal  force  exerted  by  the  body  when  not  tidally  dis- 
torted. That  is,  the  proper  centripetal  force  is  diminished. 
But  since  the  orbital  velocity  of  C  is  the  resultant  of  cen- 
trifugal and  centripetal  components,  it  will  be  diminished 
by  the  diminution  of  the  centripetal  component.  Diminu- 
tion of  orbital  velocity  diminishes  in  turn  the  centrifugal 
tendency.  So  the  body  C,  in  being  drawn  along  the  tan- 
gent C  G.  and  getting  a  little  outside  of  its  orbit,  experi- 
ences diminution  of  centripetal  force,  orbital  velocity  and 


TIDAL    ACTION    IN    PLANETARY    HISTORY  241 

centrifug'al  force.  In  other  words,  it  revolves  at  a  slightly 
greater  distance  from  the  centre  O,  and  with  a  diminished 
linear  and  angular  velocity.*  The  principle  is  precisely 
the  converse  of  that  under  which  a  resisting  medium,  in 
opposing  the  orbital  motion  of  a  body,  determines  an  ac- 
celeration of  velocity,  and  motion  in  a  smaller  orbit. 

This  reaction  of  the  tide  may  perhaps  be  more  thor- 
oughly understood  by  the  use  of  the  general  diagram, 
Figure  42.  Here  as  before,  the  crest  of  the  tide  is  at  tl 
when  the  tide-producer  is  in  the  zenith  at  m,  and  the 
action  exerted  from  t^  tends  to  accelerate  M  in  the  direc- 
tion of  r;  but  acceleration  causes  M  to  depart  from  its 
orbit  in  the  direction  of  the  tangent  M  M',  and  thus,  as 
before,  orbital  retardation  is  the  ulterior  result.  The  same 
action  takes  place  at  whatever  point  along  the  great  circle 
L  L  L  L  the  tide  may  exist  during  the  movement  of  M  for- 
ward in  its  orbit. 

A  very  high  state  of  viscosity  may  result  in  retardation 
-instead  of  acceleration  of  the  tide-producer  in  its  orbit. 
Let  the  annexed  diagram  be  a  projection  on  the  plane  of 
the  planet's  equator.  Then  when  the  lagging  of  the  tide 
amounts  to  90°,  as  at  t^,  the  anti-tide  at  t' j  exerts  an  at- 
traction on  M  which  nearly  neutralizes  the  attraction  of 
the  tide.  At  some  distance  east  of  £t,  as  at  tz,  the  attrac- 
tion exerted  upon  M  by  the  a-nti-tide,  t'z,  exceeds  the 
attraction  exerted  by  the  tide.  The  excess  of  action  of 
the  anti-tide  results  in  a  retardation  of  M;  it  is,  therefore, 
drawn  by  centripetal  action  nearer  to  the  planet,  and  its 
velocity  is  accelerated.  A  very  high  state  of  viscosity 

*  This  case  illustrates  the  interesting  fact  that  the  influence  exerted  by  an 
attracting  body  must  depend,  in  certain  positions,  upon  its  figure.  If  there  were 
no  lagging  of  the  tide  the  motion  of  the  tide-producer  would  not  be  affected : 
and  if  the  lagging  were  just  90°,  the  influence  of  the  anti-tide  would  neutralize 
that  of  the  tide.  So  the  equatorial  protuberance  of  an  oblate  spheroid  must 
exert  an  influence  on  the  motion  of  a  body  revolving  around  it,  except  when  the 
body  is  in  the  plane  of  the  protuberance,  or  exactly  in  the  line  of  the  axis  pro- 
duced—  a  relation  which  never  exists  in  our  system. 
16 


242 


A    COOLING    PLANET. 


FIG.  44.— VARYING  REACTION  RESULTING  FROM  VARYING  VISCOSITY. 


exists  at  the  surfaces  of  planetary  bodies  when  passing 
from  the  fluid  to  the  solid  state,  but  whether  it  ever  pro- 
duces sufficient  tidal  lagging  to  work  a  retardation  of  a 
satellite  is  unknown.  Undoubtedly  the  more  prolonged 
and  older  fluidic  condition,  accompanied  by  accelerative 
lagging  of  tide,  impresses  more  important  results  on  the 
life- history  of  satellites. 

This  direct  retardative  result  proceeds  from  the  influ- 
ence of  excessive  viscosity  in  any  state  of  inclination  of 
the  orbit  and  the  planetary  equator.  The  result  will  be 
reached  also,  with  a  lower  degree  of  viscosity,  in  propor- 
tion as  this  inclination  is  increased;  because  the  greater 
the  inclination  the  sooner  the  lagging  tide  is  carried  by 
the  planet's  rotation  around  to  a  point  in  the  rear  of  the 
radius  vector  of  the  tide-producer.  This  will  be  under- 
stood from  the  general  diagram,  Figure  42,  by  conceiving 
the  great  circle  L  L  L  L  to  have  such  obliquity  as  to  be 
tangent  to  the  small  circles  around  the  poles  N  and  S.  A 
tide  inaugurated  at  any  point  on  this  great  circle  will  be 
carried  nearly  at  right  angles  away  from  it  by  the  planet's 
rotation,  and  the  tidal  culmination  may  be  reached,  espe- 
cially if  the  lagging  is  great,  at  such  a  distance  that  the 
curvature  of  the  parallel  brings  the  crest  of  the  tide  to 


TIDAL   ACTION    IK    PLAXETARY   HISTORY.  243 

the  west  of  the  radius  vector  of  the  tide-producer.  It 
appears,  therefore,  that  as  the  inclination  increases,  the 
degree  of  viscosity  which  will  produce  retardation  dimin- 
ishes, and  when  the  inclination  is  90°,  acceleration  results 
under  all  degrees  of  viscosity,  when  the  tidal  crest  is  in 
the  southern  hemisphere,  while  retardation  results  when  it 
is  in  the  northern  hemisphere.  On  the  contrary,  as  the 
inclination  diminishes,  the  degree  of  viscosity  requisite  to 
produce  retardation  increases,  and  when  the  inclination  is 
zero,  the  viscosity  must  be  such  as  to  produce  a  lagging  of 
more  than  90°  of  longitude. 

(3.)  TliG  lagging  of  the  tide  increases  the  inclination 
of  the  equator  of  the  tide-bearer  to  the  orbit  of  the  tide- 
producer. — By  reference  to  the  general  diagram,  Figure 
42,  it  is  seen  that  an  attraction  exerted  by  a  body  M  upon 
a  tidal  protuberance  at  ^  imparts  not  only  a  tendency  of 
the  tide-bearer  to  rotate  backward  around  the  axis  N  S, 
but  also  a  tendency  to  rotate  around  the  axis  X  X.  In 
other  words,  the  actual  motion  of  the  tide-bearer  in  the 
direction  of  the  pull  may  be  resolved  into  two  rotations 
about  the  two  axes  named.  The  tide-producer  is  always 
vertically  over  some  point  of  the  great  circle  L  L  L  L. 
When  that  point  is  north  of  the  equator,  the  rotation  of 
the  tide-bearer  carries  the  tide  north  of  the  plane  L  L  L  L, 
and  an  attraction  exerted  from  that  plane  must  tend  to 
bring  the  tidal  crest  into  the  plane;  that  is,  to  bring  a 
point  north  of  the  plane  LLLL  southward  into  that 
plane.  The  effect  of  this  must  be  to  increase  the  inclina- 
tion of  the  axis  N  S  toward  the  axis  of  the  plane  LLLL. 
When  the  apex  of  the  tide  is  south  of  the  equator,  the 
rotation  of  the  tide-bearer  carries  it  south  of  the  plane 
LLLL,  and  an  attraction  exerted  from  that  plane  must 
tend  to  bring  the  tidal  crest  into  the  plane;  that  is,  to 
bring  a  point  south  of  the  plane  LLLL  northward  into 
that  plane.  The  effect  of  this  must  also  tilt  the  axis  of 


244  A    COOLIXG    PLAXET. 

the  tide-bearer  into  a  larger  inclination  to  the  axis  of 
L  L  L  L.  In  all  positions  of  its  orbit,  therefore,  the  tide- 
producer  increases  the  angle  formed  by  the  great  circles 
E  E  E  E  and  L  L  L  L. 

Reciprocally,  however,  the  reaction  of  the  tide  in  all 
positions  where  the  inclination  referred  to  is  increased, 
exerts  a  tendency  to  move  the  tide-producer  M  above  or 
below  the  plane  of  its  orbit.  When  the  tidal  crest  by 
lagging  is  carried  above  that  plane,  the  tide-producer  is 
drawn  above  it.  In  all  that  half  of  its  orbit  which  lies 
north  of  the  equator,  the  tendency  of  the  lagging  tide  is 
to  keep  the  tide-producer  above  the  plane  of  its  orbit.  In 
all  that  half  of  its  orbit  which  lies  south  of  the  equator, 
the  tendency  of  the  lagging  tide  is  to  keep  the  tide-pro- 
ducer below  the  plane  of  its  orbit.  That  is,  one-half  of 
the  orbit  is  elevated  and  the  other  is  depressed.  The 
inclination  of  the  orbit  is  changed  in  reference  to  a  con- 
stant plane;  say  the  fundamental  plane  of  the  planetary 
system. 

The  action  of  the  tide  in  increasing  the  angle  between 
the  axis  N  S  and  the  axis  of  L  L  L  L  would  not  result  in  a 
steady  movement  of  one  pole  from  the  other.  The  pole 
N  would  pursue  a  sinuous  course,  making  one  sweep  to 
the  east  and  one  to  the  west  at  each  semi-revolution  of 
the  tide-producing  body.  Similarly  the  path  of  this  body 
would  be  sinuous  —  moved  twice  above  its  mean  position 
and  twice  below  it  during  each  revolution. 

As  the  viscosity  of  the  tide-bearing  medium  increases, 
the  position  of  t  in  Figure  42  moves  around  farther  east 
on  the  parallel  COCO.  At  length,  with  further  suppos- 
able  increase  of  viscosity,  the  amount  of  lagging  becomes 
90°.  At  this  point  the  increase  of  obliquity  ceases. 
Beyond  this  point,  the  effect  of  lagging  is  to  diminish  the 
obliquity.  This  is  more  clearly  shown,  for  a  particular 
position  of  the  tide-producer,  in  the  annexed  diagram, 


TIDAL    ACTIOX    IX    PLAXETARY    HISTORY. 


245 


Figure  45,  where  the 
equator  and  parallels 
and  plane  of  the  orbit 
of  the  tide-producer 
(m  A)  are  seen,  from 
an  infinite  distance, 
projected  in  straight 
lines.  M  is  the  pro- 
jection of  the  tide-pro- 
ducer. When  the  pro- 
jection of  the  retarda- 
tion is  m  t,  the  effect  of  FlG  45._TlDAL  INCREASE  AND  DIMINUTION 
attraction  toward  the  OF  OBLIQUITY. 

plane  of  the  orbit  m  A, 

is  to  increase  the  inclination  of  the  axis  N  S.  When  the 
projection  of  the  retardation  is  mt^,  no  effect  is  produced. 
When  the  projection  of  the  retardation  is  mt2  or  mt3,  the 
effect  of  attraction  toward  the  plane  m  A  is  to  diminish 
the  inclination.  The  theoretical  anti-tide-producer  acts 
concurrently,  as  shown  in  this  diagram.  It  appears,  there- 
fore, that  with  a  high  state  of  viscosity  the  increase  in 
the  obliquity  may  become  nil,  or  even  changed  to  a  dimi- 
nution. 

The  three  classes  of  tidal  reactions  thus  explained  are 
reciprocal.  The  planetary  body  exerts  a  tidal  influence 
upon  the  lunar  body  as  much  greater  than  that  experi- 
enced itself,  as  its  mass  is  greater  than  that  of  the  lunar 
body;  though  the  height  of  the  tide  raised  depends  also 
on  the  radius  of  the  lunar  body,  and  the  mobility  of  its 
parts.  Since  the  lunar  body  must  be  viewed  as  always 
more  or  less  viscous,  and  on  our  theory,  must  at  some 
stage  pass  through  a  semi-fluid  state,  the  lagging  of  the 
tide  borne  by  this  body  must  tend  always  to  retard  its 
rotary  motion.  This  general  deduction  leads  us  to  some 


246 


A    COOLING    PLANET. 


very  interesting  applications  to   particular  cases,  as  will 
hereafter  be  shown. 

The  reaction  of  the  lunar  tide  upon  the  orbital  motion 
of  the  planet  around  the  common  centre  of  gravity  of  the 
two  bodies,  however  insignificant  in  amount,  is  a  sequence 
which  is  real.  Let  M,  Figure  46,  represent  a  moon,  a  the 


FIG.  46  — THE  TIDE-BEARER  VIEWED  AS  TIDE-PRODUCER. 

centre  of  gravity  of  a  planet,  and  C  the  centre  of  gravity 
between  the  moon  and  the  planet.  The  centre  of  gravity 
a  revolves  about  the  centre  of  gravity  C  in  an  orbit  a  b  c. 
On  the  moon  the  lagging  of  the  tide  brings  its  apex  to  t, 
and  this  lagging  tide  acts  on  the  centre  of  gravity  a.  As 
this  action  is  not  in  the  direction  of  the  radius  vector  a  C, 
the  tendency  is  to  accelerate  a  toward  w.  This,  as  before, 
bv  increasing  the  centrifugal  force  increases  the  distance 
from  C  to  a,  and  ends  in  retardation  of  a  in  its  orbit.  As 
the  planet  and  satellite  are  always  in  the  same  position 
in  relation  to  C,  this  action  exists  in  all  parts  of  their 
respective  orbits.  So  the  tidal  retardation  of  the  lunar- 
planetary  revolution  about  the  common  centre  C  is  the 
sum  of  the  reactions  from  the  lagging  tides  upon  the  two 
bodies. 

It  will  be  noticed  also,  that  with  a  high  degree  of  vis- 
cosity, producing  a  lagging  of  more  than  90°,  the  reaction 
upon  «  exerted  by  the  anti-tide  of  the  satellite  will  exert  a 
retarding  influence  upon  the  orbital  motion  of  a.  The  ac- 


TIDAL   ACTION    IX   PLANETARY   HISTORY.  247 

celerative  and  retardative  influences  of  planet  and  satellite 
are,  therefore,  precisely  reciprocal  and  consentaneous. 

Similarly,  it  will  appear,  on  a  moment's  consideration, 
that  if  the  axis  of  the  satellite  possesses  some  degree  of 
inclination  to  the  axis  of  the  planet's  orbit,  such  inclination 
will  be  increased  and  diminished  under  the  same  conditions 
as  increase  and  diminution  of  the  planet's  inclination  to 
the  satellite's  orbit. 

This  whole  subject  ought  to  be  contemplated  under  re- 
lations still  more  general.  Each  of  the  planets  stands  in 
the  tidal  relation  of  a  satellite  to  the  sun,  and  the  sun  is  a 
tide-producing  body  to  each  of  its  planets.  The  remote- 
ness of  the  major  planets  diminishes  this  reciprocal  action, 
perhaps,  below  the  limit  of  cosmical  importance,  but,  on 
the  contrary,  tidal  actions  within  nearer  limits  must  possess 
a  high  degree  of  importance.  The  same  kind  of  influence 
which  a  planet  exerts  upon  a  satellite,  the  sun  exerts  upon 
the  planet  itself.  That  is,  the  solar  tide  tends  to  retard 
the  planetary  rotation,  to  retard  its  angular  motion  in  its 
orbit,  and  to  increase  the  inclination  of  its  axis  to  the  axis 
of  its  orbit.  The  tide  upon  the  sun  must  tend  also  to 
draw  the  planet  out  of  the  plane  of  its  orbit,  and  thus  to 
increase  the  obliquity  of  that  plane  to  the  plane  of  the 
sun's  equator. 

We  are  thus  brought  face  to  face  with  the  striking  fact 
that  tidal  evolution  is  a  suggestive  explanation  of  many  of 
those  apparent  anomalies  which  have  been  cited  as  difficul- 
ties in  the  nebular  theory.  Inadequate  rotary  and  orbital 
velocities  may  be  thus  explained.  Inclinations  of  axes  of 
rotation  may  have  been  brought  to  a  higher  degree  —  and 
highest  upon  those  planets  most  affected  by  solar  tides. 
Even  the  inclinations  of  the  planetary  orbits  may  have 
been  increased  by  tidal  protuberances  on  a  sun  rotating  with 
some  preexisting  inclination  of  its  axis.  We  cannot,  how- 
ever, explain  all  axial  and  orbital  obliquity  in  this  way. 


248  A    COOLING    PLANET. 

Change  in  obliquity  depends  on  the  antecedent  existence 
of  some  obliquity.  With  obliquity  nil  we  have  conditions 
of  equilibrium.  There  must  have  been  other  causes  to 
inaugurate  the  obliquity  which  tidal  influence  increases. 
The  existence  of  other  causes  has  been  heretofore  pointed 
out.  (Part  II,  ch.  i,  §§  2-3.) 

3.  Tendency  to  Synchronism  of  Rotary  and  Orbital 
Motions. — We  may  now  proceed  to  trace  more  specifically 
some  necessary  deductions  from  the  physical  principles 
thus  defined.  Every  planetary  body  in  the  solar  system 
has  always  been  tidally  influenced  by  every  other  body  in 
the  system.  We  may  disregard,  however,  at  present,  the 
tidal  disturbances  excited  in  the  sun,  and  also  the  influ- 
ences of  the  primary  planets  upon  each  other.  Great  im- 
portance, however,  must  be  conceded  to  three  classes  of 
tides:  First,  The  influence  of  primaries  upon  their 
secondaries.  Second,  The  influence  of  secondaries  upon 
their  primaries.  Third,  The  influence  of  the  sun  upon 
the  planets.  The  greatest  tidal  distortion  would  result 
from  the  influence  of  a  primary  of  large  mass  upon  its 
own  satellites.  The  mass  of  Jupiter  being  three  hundred 
times  that  of  the  earth,  and  his  inner  satellite  being  but 
little  more  remote  than  our  moon  from  the  earth,  the  tidal 
influence  of  Jupiter  upon  his  inner  satellite  should  be,  for 
these  reasons,  about  three  hundred  times  as  great  as  the 
influence  of  the  earth  upon  the  moon.  But  since  this 
satellite  has  about  the  diameter  of  the  moon,  with  less 
than  half  its  mass,  the  tidal  influence  of  Jupiter  would 
become  still  more  enormous.  The  tidal  influence  of  the 
earth  upon  the  moon,  so  far  as  due  to  relative  mass,  should 
be  about  eighty  times  as  great  as  that  of  the  moon  upon 
the  earth.  The  enormous  tides  raised  upon  the  satellites 
while  in  a  primitive  aeriform,  fluid  or  semi-fluid  condition 
must  have  exerted  a  most  important  influence  upon  their 
development.  Confining  our  attention  to  the  retarding 


TIDAL   ACTION    IN    PLANETARY   HISTORY.  249 

effect,  this  must  have  had  almost  a  controlling1  power  over 
their  axial  rotations.  It  may  even  be  doubted  whether  the 
whole  process  of  shrinkage  after  the  attainment  of  a  semi- 
fluid state,  and  the  consequent  diminished  tendency  to  ac- 
celerated rotation,  has  been  sufficient  to  overcome  the 
tidal  influence  of  the  primary  in  any  single  instance,  so  as 
to  establish  for  any  epoch  an  angular  motion  more  rapid 
than  the  satellite's  orbital  motion.  As  the  moon  turns 
always  the  same  side  toward  the  earth,  it  is  reasonable  to 
infer  that  this  condition  has  been  produced  by  the  tidal  in- 
fluence exerted  chiefly  by  the  earth.  It  seems  probable, 
also,  that  the  condition  was  assumed  at  an  early  period  in 
the  moon's  history,  even  if  a  non-synchronous  rotation 
had  once  been  established  during-  an  earlier  aeriform  period 
when  freer  mobility  of  parts  gave  the  moon  somewhat  the 
character  of  a  perfect  fluid,  in  which  tidal  lagging  would 
not  take  place.  So  far  as  we  can  judge  from  observation, 
other  satellites  have  attained  a  similar  state  of  synchronistic 
motions;  and  this  is  certainly  in  accordance  with  our 
reasoning. 

A  reciprocal  though  greatly  inferior  influence  is  exerted, 
or  has  been  exerted,  by  each  satellite  upon  its  primary. 
During  the  plastic  condition  of  the  primary,  the  deforma- 
tive  tide  must  lag,  and  a  retarding  effect  must  result. 
Each  planet  has  been  strained  to  desist  from  its  rapid 
rotation,  and  present  constantly  the  same  side  toward  its 
most  powerful  satellite.  Without  the  least  doubt  this 
influence,  continued  through  millions  of  years,  has  mate- 
rially retarded  the  rotary  motions  of  the  planets.*  Those 

*Kant,  the  great  thinker,  whose  sagacity  can  scarcely  be  too  much  re- 
spected, was  the  first  to  make  note  of  these  reciprocal  tidal  actions  on  the 
earth  and  moon.  See  his  prize  essay,  presented  in  1754  to  the  Berlin  Academy 
of  Sciences,  entitled :  Untersuchung  der  frage,  ob  die  Erde  in  ihrer  Umdrehung 
um  die  Achse,  wodurch  sie  die  Abwechselung  des  Tages  und  der  Nacht  hervor- 
bringt,  etnige  Veranderung  seit  den  ersten  Zeiten  Ihres  Ursprunges  erlitten  habe, 
und  woraus  man  sich  ihrer  versichern  konne. 


250  A   COOLTXG   PLAXET. 

planets  would  be  most  retarded  whose  masses  sustain 
lowest  relations  to  the  masses  of  their  satellites  —  allow- 
ance being  made  also  for  distances.  The  earth,  and  possibly 
Mars,  should  have  departed  most  from  their  primitive 
axial  velocities ;  Jupiter  and  the  exterior  planets  least. 
But  Venus  and  Mercury  being  unprovided  with  satellites, 
have  been  unaffected  by  their  influence.  Observation  has 
not  certainly  shown  what  is  their  actual  rate  of  rotation. 

The  tidal  influence  exerted  by  the  satellites  upon  the 
planets  would  be  reinforced  by  the  sun's  influence  upon 
them.  At  the  distance  of  the  earth,  the  solar  tidal  effi- 
ciency is  two-fifths  that  of  the  moon  upon  the  earth.  At 
the  distance  of  Venus  the  solar  tidal  efficiency  is  one  and 
two-fifths  times  as  great  as  at  the  earth  ;  which  gives 
at  Venus  a  solar  tide  two-thirds  as  great  as  the  lunar  tide 
upon  the  earth.  At  Mercury  the  solar  tidal  efficiency  is 
17.44  times  as  great  as  upon  the  earth,  which  is  6.976 
times  as  great  as  our  lunar  tide.  These  two  planets, 
therefore,  while  exempt  from  the  retarding  influence  of 
satellites,  have  suffered  very  important  retarding  influ- 
ences exerted  by  the  sun.  It  would  not  be  a  stretch  of 
probability  to  conclude  that  Mercury,  at  least,  has  attained 
already  a  state  of  synchronistic  axial  and  orbital  motions, 
even  if  such  state  has  not  existed  from  the  gaseous  epoch 
of  the  planet's  evolution. 

At  a  later  period  in  a  planet's  career,  after  approxi- 
mate rigidity  has  diminished  greatly  the  retarding  influ- 
ence of  deformative  tides,  the  tidal  disturbance  of  the 
fluids  on  their  surfaces  maintains  a  frictional  retardative 
action  which  continues  the  tendency  to  synchronistic  mo- 
tions. Whenever  a  planetary  surface  becomes  covered 
with  a  film  of  water,  interrupted  in  places  by  protruding 
portions  of  the  solid  nucleus,  then  all  tidal  movements 
of  the  water  along  the  shores  of  islands  and  continents, 
and  over  bottoms  not  beneath  the  influence  of  such  dis- 


TIDAL   ACTION   IN    PLANETARY   HISTORY.  251 

turbances,  is  met  by  resistances  which  tend  to  destroy  the 
motions.  As  the  resultant  of  all  the  tidal  motions  is 
toward  the  west,  the  rotary  motion  of  the  tide-bearer  is 
continually  diminished,  and  continually  approaches  syn- 
chronism with  the  orbital  motion  of  the  tide-producer. 
Thus  the  earth  is  tending  to  settle  into  such  a  rate  of 
rotation  that  one  side  will  always  be  turned  toward  the 
moon.  After  this  condition  shall  have  been  reached,  the 
solar  tide  will  further  retard  its  rotation  toward  the  limit 
where  the  same  side  will  be  turned  constantly  toward  the 
sun.  Meantime,  however,  after  a  planet's  rotation,  by  this 
influence,  becomes  slower  than  the  orbital  revolution  of  its 
satellite,  a  lunar  tide  will  spring  up  again,  lagging  behind 
the  satellite,  and  tending  to  accelerate  the  planet's  rota- 
tion. If  the  lunar  tide  should  now  retain  all  its  former 
magnitude,  the  satellite  would  prevail  over  the  sun,  and 
prevent  final  synchronism  with  the  sun.  But  the  satellite, 
as  has  been  explained,  has  receded  from  its  planet,  and  its 
tide  has  diminished  as  the  cube  of  the  distance  increased. 
Besides,  the  amount  of  lagging  now  is  less,  since  the  sat- 
ellite passes  the  planet's  meridians  more  slowly.  Thus 
the  power  of  the  satellite  may  not  be  able  to  cope  with 
that  of  the  sun,  and  the  planet  may  ultimately  turn  the 
same  side  continually  toward  the  sun. 

Whenever  a  body  is  brought  to  turn  the  same  side  con- 
stantly toward  a  tide-producer,  then  some  important 
changes  must  take  place  in  the  distribution  of  the  fluids 
upon  its  surface.  Not  only  will  a  state  of  permanent 
bodily  deformation  result,  and  thus  all  mechanical  devel- 
opment of  internal  heat  be  arrested,  but  now  all  the  fluids 
will  dispose  themselves  on  the  remoter  side  of  the  body. 
Thus  all  the  water  would  be  displaced  from  the  nearer 
pole  of  the  prolate  axis,  and  accumulated  about  the 
remoter  one.  The  atmosphere  would  also  be  similarly 
distributed.  No  body  thus  fixed  in  its  position  should 


252  A    COOLING    PLAXET. 

therefore  present  any  seas,  or  perhaps  atmosphere,  to  the 
view  of  an  observer  placed  on  the  tide-producer  which 
controls  its  rotation.  This  supposes,  however,  that  these 
fluids  exist  in  nearly  the  same  proportion  to  the  body  as 
on  the  earth.  But  we  shall  discover  hereafter  another 
cause  of  the  disappearance  of  water  and  atmosphere. 

4.  Predetermination  of  Sub-meridional  Trends. —  In 
the  early  incrustive  periods  of  a  planet's  existence,  the 
tidal  disturbance  would  determine  some  permanent  fea- 
tures of  the  surface.  It  seems  to  me  that  some  meridio- 
nal disposition  of  the  structure  of  the  crust  would  arise 
without  the  intervention  of  the  retral  translatory  motion 
already  considered  in  its  general  features.  The  tidal  wave 
would  be  an  immense  swell  of  the  liquid  portion  stretching 
meridionally  from  high  northern  to  high  southern  latitudes. 
It  would  indeed,  have  a  corresponding  breadth  from  east 
to  west.  Its  progressive  changes  of  position,  however, 
would  be  across  the  meridians.  The  successiveness  of 
similar  tidal  conditions  and  effects  would  extend  from  east 
to  west.  This  would  be  true  of  parallels  north  and  south 
of  the  zenith  positions  of  the  tide-producing  body,  as  well 
as  of  those  experiencing  the  maximum  tidal  influence. 
Simultaneousness  of  tidal  conditions  and  effects  would 
extend  meridionally.  The  progressive  westward  changes 
in  the  position  of  the  swell  must  determine  arrangements 
of  the  rising  and  sinking  fragments  having  relation  to 
the  direction  of  the  progress.  Parts  along  the  same  me- 
ridian would  sustain  identical  relations  to  the  direction  of 
the  progress,  and  receive  an  identical  and  simultaneous 
impress.  Though  the  next  meridian  would  be  immedi- 
ately visited  by  the  same  action,  it  would  be  the  simulta- 
neous results  rather  than  the  successive  ones,  which  would 
determine  zones  of  homogeneous  structure  or  similar  con- 
dition, like  the  lines  of  growth  over  the  surface  of  a 
sea-shell.  Accessory  causes  would  be  joined  to  these  influ- 


TIDAL   ACTION    IX    PLANETARY    HISTORY.  253 

ences.  Whatever  effects  might  result  from  the  conjunc- 
tion of  any  casual  influences  with  tidal  action,  would  arise 
simultaneously  along  meridional  lines  more  or  less  ex- 
tended.* Such  casual  influences  might  originate  in  storms 
or  special  conditions  of  the  crust.  It  is  reasonable  to 
suppose,  therefore,  that  the  tides  would  impress  some 
characteristics  of  surface  meridionally  disposed. 

But  there  is  a  stronger  reason  for  supposing  this,  as 
has  been  shown.  The  inertia  of  the  tidal  mass  and  the 
friction  of  moving  parts  upon  each  other  would  cause  the 
summit  of  the  swell  to  linger  somewhat  behind  the  me- 
ridian passage  of  the  tide-producing  body.  This  body 
would  therefore  exert  constantly  some  force  of  displace- 
ment tending  to  give  the  tidal  mass  a  slight  motion  of 
translation  opposite  to  the  direction  of  the  rotation  of  the 
tide-beaYing  body.  Whatever  translatory  motion  of  the 
tide  wave  might  result  —  whatever  pressure  might  be 
exerted  by  a  tendency  toward  translatory  motion,  would 
be  an  effect  which,  combining  with  the  casual  influences, 
would  still  more  distinctly  impress  meridional  features 
upon  the  constitution  and  structure  of  the  solidifying 
crust.  The  tendency  to  translatory  motion  may  be  very 
slight;  the  aggregate  impression  of  all  these  causes  may 
be  slight;  but  if  these  are  real  physical  causes  they  may 
aggregate  enough  to  turn  a  balance  of  conditions,  and 
leave  on  the  surface  of  the  solidified  planet  some  record 
of  their  existence. 

In  the  early  incrustive  stages  this  tide  would  not  only 
break  the  forming  crust  into  a  mass  of  angular  and  after- 
ward rounded  fragments,  but  would  initiate  some  ten- 
dency to  westward  motion  for  certain  distances.  When 

*  Transmeridional  features  might  indeed  be  created  by  any  influence 
changing  its  point  of  application  in  the  direction  of  the  tidal  motion,  as  we  find 
upon  the  exterior  of  a  sea-shell  lines  of  structure  transverse  to  the  lines  of 
growth,  and  sustaining  relations  to  causes  which  move  in  the  direction  of  the 
growth. 


254  A    COOLING 

this  tendency  should  be  finally  overcome  by  aggregated 
resistances,  the  fragments  would  be  left  in  long  ranges 
meridionally  disposed,  which,  though  incomparably  less 
pronounced,  might  be  compared  to  the  windrows  of  ice- 
blocks  piled  along  the  shore  by  the  swell  upon  the  surface 
of  one  of  the  great  lakes.  Thus  a  certain  predisposition 
to  meridional  trends  would  be  induced. 

At  a  later  stage,  when  a  continuous  floe-like  crust 
should  have  come  into  existence,  the  same  tidal  swell  would 
raise  the  crust  in  broad  billows  which  would  continually 
change  their  position  westward  on  new  belts  of  crust. 
Whatever  action  should  be  exerted  —  whatever  effects 
produced,  they  would  range  meridionally,  and  this  effect 
would  be  reinforced  by  the  tangential  component  of  the 
tidal  action.  Thus  the  crust  would  come  into  existence 
with  ingrained  meridional  features  in  its  structure,  and 
with  predetermined  aptitudes  to  assume  new  features  hav- 
ing the  same  general  trend.  If,  subsequently,  any  cause 
should  necessitate  the  development  of  wrinkles  in  the 
crust,  the  earliest  ones  must  naturally  assume  meridional 
trends.  Such  trends  once  inaugurated,  others  parallel 
with  them  would,  by  a  double  necessity,  come  into  exist- 
ence if  the  wrinkling  process  should  continue.  Thus  all 
the  primitive  wrinkles  should,  under  a  general  law,  ex- 
hibit trends  across  the  parallels.  At  later  periods,  after 
an  advanced  differentiation  of  the  planetary  surface,  sec- 
ondary causes  might  induce  wrinkles  and  folds  of  the  crust 
trending  in  other  directions.  Great  interest  arises  in  the 
application  of  these  principles  to  the  case  of  the  earth. 

In  these  statements  concerning  the  inauguration  of 
meridional  trends  I  have  said  nothing  concerning  the  dif- 
ferential retrograde  slipping  of  the  equatorial  regions 
and  those  situated  to  the  north  and  south  of  the  equator. 
It  will  be  borne  in  mind,  however,  that  the  tangential  com- 
ponent of  the  tidal  force  is  most  effective  at  the  crest  of 


TIDAL   ACTION    IN    PLANETARY    HISTORY.  255 

the  tide.  It  follows,  therefore,  that  the  structural  features 
thus  far  referred  to  as  meridional  would  tend  to  assume, 
north  of  the  equator,  a  trend  somewhat  northeasterly,  and 
south  of  the  equator  a  trend  somewhat  southeasterly.* 

5.  Outflow    of  Molten   Matter. — The  tidal  elevation 
and   depression  of    the   planetary   crust   would    not   only 
cause  extensive  fractures,  but  would  furnish  occasion  for 
the  outflow  of   molten   matter  through   the  vents.     It  is 
certain  that  the  effort  of   the   underlying  liquid  to  rise 
higher  than  the  partially  rigid   crust   would   rise,   would 
cause   the   fluid   to   escape   through   any   fractures  which 
might  exist,  and  overflow  the  surrounding  surface.     This 
fluid  solidifying  around  the  border,  would  eventually  build 
up  a  crater-like  elevation  of   any  assignable  magnitude. 
In  later  periods,  upon  a  planet  supplied  with  the  condi- 
tions   of    extensive    denudation,    these   crateriform   emi- 
nences might  disappear;  while  on  a  planet  not  supplied 
with    the  conditions   of   denudation,  they  might    remain 
indefinitely.     These  principles  have  a  very  important  ap- 
plication in  the  case  of  the  moon. 

6.  Crushing  Effects  of  Tidal  Reformation. — Planet- 
ary tides  would  never  cease  to  be  felt.     A  planet  would 
never  become  so  solid  as  not  to  yield  to  an  influence  as 
powerful,  for   instance,   as  that  which    the   moon    exerts 
upon  the  earth.     The  tide  would  be  a  perpetually  shifting 
deformation  of  the  solid  parts  of  the  planet.     This  must 
necessarily  be   accompanied    by  extensive   molecular  dis- 

*  Although  the  establishment  of  primitive  meridional  trends  was  worked 
out  by  me  independently,  I  am  indebted  to  Mr.  G.  H.  Darwin  for  the  suggestion 
that  these  trends  would  make  an  angle  with  the  meridian.  See  his  highly  in- 
teresting memoir  on  Problems  Connected  ivith  the  Tides  of  a  Viscous  Spheroid, 
read  before  the  Royal  Society  of  London,  December  19,  1878.  Phil.  Trans.,  Pt. 
II,  1879.  Mr.  Darwin  shows  that  each  point  of  the  planet's  surface  moves  from 
east  to  west  with  a  linear  velocity  proportional  to  the  cube  of  the  distance  from 
the  axis,  and  the  parts  north  of  the  equator  change  their  longitude  from  wtst  to 
east  relatively  to  the  equator,  at  a  rate  proportional  to  the  square  of  the  sine  of 
the  latitude. 


256  A    COOLING    PLANET. 

placement.  It  is,  in  effect,  a  crushing  agency,  and  the 
consequence  must  be  the  development  of  an  enormous 
amount  of  heat.  It  would  appear,  therefore,  that  even 
after  a  planet  should  have  been  chilled  to  its  centre,  tidal 
deformation  must  continue  to  produce  the  phenomena  of 
internal  heat.  Until  the  time  should  arrive  when  the  same 
side  is  turned  continually  toward  the  tide-producing  body, 
the  progressive  transfer  of  the  tidal  swell  would  produce 
at  any  given  point  not  too  near  the  poles,  periodical 
movements  of  the  planetary  crust.  The  daily  effects  of 
these  disturbances  might  in  part  be  stored  up  in  the  form 
of  strains  and  tensions  which,  modified  and  probably  in- 
tensified by  general  shrinkage,  would,  at  longer  and  at 
irregular  intervals,  become  too  great  for  the  planetary 
structure  to  endure,  and  would  thus  eventuate  in  sudden 
and  violent  uplifts  or  collapses,  and  at  times,  in  the  open- 
ing of  vents  for  the  escape  of  internal  heated  substances. 
These  violent  strains  and  sudden  movements  would  be 
most  likely  to  occur  after  the  attainment  of  a  high  state 
of  rigidity  in  the  crust,  and  the  formation  of  permanent 
inequalities  of  considerable  magnitude. 

7.  Marine  Tides  in  the  Early  History  of  a  Planet. — 
The  marine  tides  produced  in  the  early  history  of  a  planet 
must  sustain  important  cosmogonic  relations.  It  has  been 
already  stated  that  the  friction  of  marine  tides  upon  shores 
and  the  bottom  of  shoals  must  tend  to  diminish  the  velo- 
city of  a  planet's  axial  rotation.  It  has  also  been  main- 
tained that  a  similar  result  must  ensue  from  the  tidal 
effects  produced  in  a  viscid  or  even  a  solid  planet,  if  not 
possessed  of  complete  rigidity.  As  this  cause  of  retarda- 
tion is  operative  in  every  planet  subjected  to  tidal  action, 
it  is  supposable  that  the  rotational  velocity  of  any  particu- 
lar planet  was  higher  in  former  periods  than  at  present. 
As  the  rate  of  retardation  must  have  been  inversely  as  the 
ratio  of  the  masses  of  the  planet  and  its  tide-producing 


TIDAL   ACTION    IX    PLANETARY    HISTOEY.  257 

satellite  or  satellites  (as  well  as  inversely  as  the  cube  of 
the  distance)  it  may  be  inferred  that  smaller  planets,  other 
things  being  equal,  have  suffered  greater  retardation  than 
larger  ones.  The  more  rapid  rotation  of  the  larger  planets 
of  our  system  is  in  accord  with  this  view. 

If  the  rotational  velocity  of  the  earth  is  thus  in  process 
of  diminution,  from  what  rate  of  velocity  did  the  diminu- 
tion begin?  According  to  the  theory  set  forth  in  this 
work,  the  earth's  rotary  velocity  was  once  such  that  the 
centrifugal  tendency  on  the  equator  was  equal  to  the  force 
of  central  gravitation,  and  at  that  time  the  matter  of  the 
moon  separated  as  a  nebulous  ring.  An  equilibrium  of 
centripetal  and  centrifugal  tendencies  would  be  reached 
at  the  present  terrestrial  equator  if  the  earth's  rotation 
were  increased  seventeen  times.*  But  in  the  nebulous 
condition  in  which  annulation  is  supposed  to  have  taken 
place,  the  radius  of  the  earth's  mass  was  much  greater 
than  at  present,  and  hence  the  physical  conditions  of 
annulation  would  have  been  supplied  by  a  much  slower 
rate  of  rotation.  The  present  radius  of  the  moon's  orbit 
cannot  be  assumed  as  the  earth's  radius  at  the  epoch  of 
annulation,  since,  as  has  been  shown,  the  moon  is  now  in 
progress  of  recession  from  the  earth,  and  must  have  been 
so  ever  since  the  commencement  of  lunar  tides  on  the 
earth's  surface.  Lunar  tides  must  have  begun  as  soon  as 
the  moon  acquired  a  separate  existence  in  such  form  that 

*  Let  /  =  present  centrifugal  tendency  at  the  equator,  the  time  of  rotation 
being  t. 

f—  centrifugal  tendency  when  the  time  of  rotation  is  V. 
g  =  present  force  of  gravity  at  the  equator. 
g'=  force  of  gravity  in  the  absence  of  any  rotation. 

Then,  since,  in  the  same  sphere,  the  centrifugal  tendency  is  inversely  as 
the  square  of  the  time  of  rotation, 


since  /'  is  to  become  equal  to  g'.    But  the  physical  constant 

/  =  0.111255,  and  g'=  32.200795, 

whence  t*=    .003455  <2=  ^  V*  nearly, 

and  t'=    .05878  t    =  TV  t  nearly  =  1.41138  hours. 

17 


258  A   COOLING   PLANET. 

its  attraction  was  not  exerted  equally  and  simultaneously 
upon  all  meridians  of  the  equatorial  belt.  A  ring  having 
its  mass  uniformly  distributed  would  not  produce  a  proper 
tide,  though  it  would  produce  an  annular  elevation  around 
the  earth.  But  as  soon  as  the  centre  of  mass  in  the  ring 
should  cease  to  coincide  with  the  geometrical  centre,  a 
tidal  action  would  begin  ;  and  this  would  increase  until 
the  annulus  should  have  become  a  spheroid.  It  seems 
entirely  probable  on  physical  grounds,  that  definite  tidal 
action  began,  and  that  even  the  lunar  spheroid  began  its 
work,  when  the  lunar  mass  was  much  nearer  the  earth 
than  at  present.  Guided  by  physical  laws  the  geognostic 
student  must,  therefore,  bear  in  mind  the  probability  of 
some  extraordinary  tidal  action  in  the  early  periods  of  the 
earth's  history. 

Mr.   G.   H.   Darwin  has  developed  in  this  connection 
some  views  of  novel  originality  and  interest.*     Proceed- 

*The  following  are  Mr.  Darwin's  principal  memoirs: 

1.  On  the  Bodily  Tides  of  Viscous  Spheroids.    Proc.  Roy.  Soc.,  May  23, 
1878;  abstract,  Nature,  xviii,  265-6,  July  4,  1878. 

2.  On  the  Precession  of  a  Viscous  Spheroid.    British  Assoc.,  Dublin  Meet- 
ing, 1878;  abstract,  Nature,  xviii,  580-2. 

3.  On  the  Precession  of  a  Viscous  Spheroid,  and  on  the  Remote  History  of 
the  Earth  (with  the  following): 

4.  Problems  Connected  with  the  Tides  of  a  Viscous  Spheroid.    Proc.  Roy. 
Soc.,  Dec.  19,  1878  (Phil.  Trans.,  Pt.  2,  1879);   abstract,  Nature,  xix,  242-3,  Jan. 
30, 1879. 

5.  On  the  Secular  Effects  of  Tidal  Friction.  Proc.  Roy.  Soc.,  June  19,  1879; 
abstract,  Nature,  xx,  246-7,  July  10,  1879. 

6.  On  the  Secular  Changes  in  the  Elements  of  the  Orbit  of  a  Satellite  Revolv- 
ing about  a  Planet  Distorted  by  Tides.    Proc.  Roy.  Soc.,  Dec.  18,  1880  (Phil. 
Trans.,  Pt.  2,  1880,  p.  731);  abstract,  Nature,  xxi,  235-7,  Jan.  8,  1880,  erratum, 
p.  276. 

7.  On  the  Tidal  Friction  of  a  Planet  At/ended  by  Several  Satellites  and  on  the 
Evolution  of  the  Solar  System.    Proc.  Roy.  Soc.,  Jan.  20, 1881 ;  abstract,  Nature, 
xxiii,  389-90. 

8.  On  the  Stresses  Caused  in  the  Interior  of  the  Earth  by  the  Weight  of 
Continents  and  Mountains.    Proc.  Roy.  Soc.,  June  16,  1881;  abstract,  Nature, 
xxiv,  831,  July  7,  1881. 

9.  On  the  Geological  Importance  of  the  Tides,  Nature ,  xxv,  213-4,  Jan.  5. 
1882. 

10.  The  Movements  of  Jupiter's  Atmosphere,  Nature,  xxx,  360-1,  Feb.  16, 


TIDAL   ACTION    IN    PLANETARY    HISTORY.  259 

ing  from  the  starting  point  already  determined  by  the 
researches  of  Ferrel  (1853),  Helmholtz,  Purser,  Sir  Will- 
iam Thomson  and  Delaunay,  Mr.  Darwin  has  attempted  to 
retrace  the  course  of  tidal  retardation  of  the  earth's  rotary 
motion  through  the  long  j»ons  of  the  past.  Having  shown 
that  the  recession  of  the  moon  must  keep  pace  with  the 
retardation  of  the  earth,  it  follows  that  at  some  epoch  in 
the  past  the  moon's  distance  was  but  a  fraction  of  its 
present  distance,  and  the  lunar  month  was  a  correspond- 
ing fraction  of  the  present  month.  The  velocity  of  the 
earth's  rotation  was  then  much  greater  than  at  .present, 
but  not  in  the  same  ratio  as  the  moon's  orbital  period  was 
less.  Hence  the  lunar  month  contained  less  than  twenty- 
seven  days.  Tracing  the  relations  of  these  motions  far- 
ther and  farther  back,  we  find  them  approximating  nearer 
and  nearer  to  equal  periods,  and  Mr.  Darwin  finds  that 
this  synchronism  must  have  existed  at  the  time  when  the 
moon's  distance  was  about  the  sum  of  the  two  radii.  He 
is  led  therefore  to  assume  as  the  basis  of  a  remarkable 
series  of  conclusions,  that  the  moon  actually  did  separate 
from  the  earth  after  the  earth  had  attained  the  condition 
of  a  molten  or  plastic  mass.  The  period  of  rotation  of  the 
earth  at  that  epoch  was,  as  he  calculates,  between  two  and 
four  hours,  and  he  assumes  it  at  three  hours.  The  epoch 
was  not  less  than  fifty-two  million  years  ago  —  probably 
much  more.  That  the  earth's  rotational  period  could  not 
have  been  less  than  about  three  hours  is  manifest  from 
the  fact  that  a  higher  rate  of  rotation  would  have  caused 
it,  in  the  condition  then  existing,  to  fly  into  pieces,  and 
the  parts  to  separate  from  each  other. 

This  is  the  juncture  at  which  he  supposes  the  moon  to 
have  originated  from  the  plastic  mass.  But  why  did  the 
terrestial  mass  separate  into  two  parts  so  unequal,  instead 
of  many  parts  ?  The  influence  of  solar  tidal  action  must 
furnish  the  explanation.  The  sun  was  already  in  existence 


260  A    COOLING    PLANET. 

before  the  moon,  and  a  solar  tide  rolled  around  the  nascent 
earth  before  it  ever  felt  the  lunar  tide.  The  solar  tide  was 
comparatively  diminutive,  but  it  was  real.  The  day  being 
three  hours  long,  each  meridian  experienced  a  solar  tidal 
swell  every  ninety  minutes.  There  existed  at  every  point 
affected  by  this  tide  a  vertical  oscillation  having  a  period 
of  ninety  minutes.  But  this  is  the  period  of  natural  oscil- 
lation or  swing  of  the  earth-mass.  Every  mass  has  a  cer- 
tain period  within  which  an  oscillation  or  swing  would 
naturally  be  accomplished,  and  its  successive  oscillations, 
like  those  of  a  pendulum,  would  be  performed  in  equal 
times.  The  rate  of  oscillation  depends  on  mass,  viscosity 
and  elasticity.  A  mass  as  large  as  the  earth  would  com- 
plete its  swing  in  a  period  comparatively  long.  Consider- 
ing it  as  a  viscid  body,  calculation  shows  that  its  gravita- 
tional oscillation  would  be  completed  in  about  ninety 
minutes.*  Now,  suppose  the  tidal  movement  to  coincide 
with  the  oscillation  period;  the  rise  and  fall  of  the  tide 
must  tend  to  establish  oscillations  in  the  earth-mass.  The 
tidal  elevation  would  concur  with  the  natural  swing  of  the 
earth-mass;  and,  at  a  time  when  the  centrifugal  tendency 
was  nearly  equal  to  gravity,  the  concurrence  of  the  tidal 
and  oscillatory  movements  might  quite  overcome  gravita- 
tion, and  the  tidally  elevated  mass  might  completely 
separate  from  the  earth.  As  only  the  tidally  elevated 
portion  of  the  earth  would  be  subjected  to  this  joint 
influence,  only  this  portion  would  separate,  and  the  earth 
would  not  fly  to  pieces.f  The  rotary  velocity  which  would 

*  Rev.  O.  Fisher  says  font  or  five  hours.    Nature,  xxv,  243. 

1 1  suspect  a  fallacy  in  this  mode  of  reasoning.  It  might  be  correct  if  the 
solar  tidal  force  conld  be  conceived  as  applied  successively  upon  the  same  side 
of  the  earth  with  intermissions  every  ninety  minutes.  An  oscillation  is  a  motion 
of  matter  in  a  definite  direction.  It  must  persist  until  a  natural  period  is  com- 
pleted. The  solar  tide,  when  the  sun's  declination  was  xero,  produced  motions 
immediately  successive  in  every  direction  around  the  circumference  of  the  equa- 
torial zone.  How  could  such  motions  generate  a  vibration  of  the  earth?  An  in- 
cipient vibration  generated  by  the  tidal  influence  in  a  certain  direction  at  one 


TIDAL   ACTION    IN    PLANETARY   HISTORY.  261 

disrupt  the  earth  as  a  whole  into  many  pieces  did  not  quite 
exist. 

That  two  moons  did  not  originate  from  the  tide  and 
anti-tide  may  be  explained  by  the  inferior  elevation  of  the 
anti  tide.  It  might  be  further  explained  on  the  principles 
just  set  forth  if  it  could  be  shown  that  the  period  of  the 
earth-oscillation  was  three  hours  instead  of  ninety  minutes. 

Such,  according  to  Darwin's  theory,  must  be  regarded 
as  the  probable  beginning  of  the  lunar-terrestrial  history. 
We  might  speculate  as  to  the  antecedents  of  this  rapid 
rotation.  The  earth  in  cooling  and  shrinking  from  a 
nebulous  state  must,  on  the  principle  of  equal  areas,  have 
undergone  great  rotary  acceleration.  This  would  be  true 
whether  the  moon  was  disengaged  as  a  nebular  annulus, 
or  later  by  a  tidal  disruption,  as  just  explained.  But  we 
are  not  in  possession  of  data  enabling  us  to  determine  cer- 
tainly which  possible  origin  of  the  moon  has  been  realized. 
There  are,  however,  so  many  analogies,  and  so  many  phys- 
'ical  considerations  pointing  to  the  origin  of  planetary  and 
lunar  masses  through  a  stage  of  annulation,  that  there 
seem  to  be  good  grounds  for  doubting  whether  Mr.  Dar- 
win's primitive,  though  plausible,  assumption  represents 
an  actual  chapter  in  the  evolution  of  the  lunar-terrestrial 
mass.  The  doubt  is  strengthened  by  the  impossibility  of 
establishing  a  similar  inference  in  the  case  of  other  planets. 

Some  special  considerations,  however,  bear  upon  the 
question.  The  disengagement  of  a  satellite,  whether 

moment,  would  be  destroyed  the  next  moment,  by  a  change  in  the  direction  of 
the  pull,  and  the  inauguration  of  a  new  vibration  in  the  changed  direction.  It 
would  seem  that  the  oscillativc  capacity  of  the  earth  must,  be  nugatory  at  the 
crisis  of  a  lunar  birth.  Nor  does  this  adjunct  appear  necessary.  If  the  moon 
originated  as  supposed,  the  solar  tide  alone  was  sufficient  to  determine  the  isola- 
tion of  a  mass.  The  centrifugal  tendency  continuing  to  increase,  the  time  would 
arrive  when  gravitation  would  be  overbalanced.  It  would  of  course  be  the  most 
protuberant  part  of  the  equatorial  belt  which  would  first  reach  and  pass  the  limit 
of  equilibrium.  That  is,  the  mass  uplifted  in  a  solar  tide  must  necessarily  be  the 
mass  detached,  regardless  of  any  measure  of  oscillation  in  the  earth. 


262  A   COOLING   PLANET. 

through  annulation  or  disruption,  takes  place  when  the 
rotational  velocity  of  the  planet  has  attained  that  crisis  in 
which  the  equatorial  centrifugal  tendency  equilibrates  the 
gravitational.  As  the  result  of  contraction,  the  rotational 
velocity  increases,  and  the  equilibrating  rate  is  continually 
approximated.  But  meantime,  two  other  actions  are  in 
progress,  one  of  which  opposes  and  the  other  limits  the 
occurrence  of  a  secondary  birth.  Solar  tides  always  exist, 
and  they  always  neutralize  to  some  extent  the  tendency  to 
accelerated  rotation.  And  further,  the  process  of  cooling 
and  condensation  ultimately  reduces  the  planet  to  a  condi- 
tion of  fluidity,  viscosity  or  solidity,  in  which  the  rate  of 
rotation  required  for  the  disengagement  of  a  satellite  is  so 
high  that  the  formation  of  a  satellite  is  no  longer  probable. 
Now,  in  planets  near  the  sun,  where  the  solar  tidal  action 
is  great,  we  may  easily  conceive  that  the  retarding  action 
has  been  so  strong  that  the  requisite  rotational  velocity 
for  the  disengagement  of  a  satellite  was  never  attained. 
Accordingly,  Mercury  and  Venus  are  without  satellites. 
On  the  other  hand,  in  the  remote  situations,  where  the 
solar  tidal  action  is  feeble,  the  rotary  acceleration  may 
have  been  so  little  impeded  that  two  or  more  lunar  births 
may  have  occurred  before  the  planet  passed  the  anniilating 
phase  of  matter.  This  is  the  more  likely  from  the  superior 
energy  of  rotation  possessed  by  larger  masses.  Accord- 
ingly, from  Mars  to  Neptune,  we  observe  planets  attended 
by  several  moons.  Between  these  two  regions,  that  is,  in 
the  zone  occupied  by  the  earth,  the  influence  of  the  solar 
tide  may  have  been  such  as  to  delay  the  crisis  until  the 
planet  had  reached  the  molten  or  viscous  stage.  It  is  not 
impossible,  therefore,  that  the  circumstances  of  the  disen- 
gagement of  our  moon  were  different  from  those  existing 
in  the  case  of  other  moons.  It  may  be  that  our  moon  was 
thrown  off  from  the  semi-fluid  terrestrial  sphere,  while  the 
other  moons  of  our  system  passed  through  the  annular 


TIDAL    ACTIOX    IX    PLANETARY    HISTORY.  263 

stage.  There  are  some  good  grounds,  at  least,  as  Mr.  G. 
H.  Darwin  has  shown,  for  supposing  our  moon  originated 
as  described.  It  is  a  curious  fact,  as  the  same  mathemati- 
cian has  shown,  that  similar  reasoning  does  not  show  that 
the  satellites  of  Mars,  Jupiter  and  Saturn  originated  in  a 
similar  way.* 

However  the  question  of  the  annular  origin  of  our 
moon  may  be  decided,  we  have  adequate  reason  for  believ- 
ing that  the  earth  and  moon- were  formerly  in  such  rela- 
tions that  the  lunar  tidal  effect  was  very  much  greater  than 
at  present.  On  the  Darwinian  premises,  Professor  Robert 
S.  Ball,f  of  Dublin,  has  lately  advanced  the  opinion  that 
enormous  lunar  tides  were  produced  upon  the  earth  dur- 
ing the  Pala?ozoic  ages.  He  thinks  it  not  unreasonable 
to  suppose  that  during  Palaeozoic  time  the  moon's  dis- 
tance was  not  over  one-sixth  of  its  present  distance  from 
the  earth.  As  the  moon's  tide-producing  effect  is  in- 
versely as  the  cube  of  the  distance,  at  one-sixth  of  the 
present  distance  the  effect  must  have  been  216  times  as 
great  as  at  present.  If,  therefore,  the  modern  oceanic 
lunar  tide  is  assumed  as  three  feet,  the  oceanic  tide  with 
the  moon  only  40,000  miles  distant,  must  have  risen  648 
feet.}:  Such  a  conception  is  startling.  Such  a  rise  and 
fall  of  the  ocean-level  along  a  continental  shore  would 
pour  over  the  land  twice  a  day  a  volume  of  water  whose 
power  and  destructiveness  it  is  impossible  to  picture. 
Such  a  rise  in  the  Atlantic  Ocean  would  send  a  flood  up 

*G.  H.  Darwin,  Proc.  Boy,  Soc.,  Jan.  20, 1881. 

t  In  a  lecture  delivered  before  the  "Midland  Institute,1'  Birmingham,  Eng- 
land, October  24,  1881,  and  published  in  Nature,  xxv,  79-82,  103-7,  Nov.  24  and 
Dec.  1,  1881.  Prof.  Ball  is  Andrews  Professor  of  Astronomy  in  the  University 
of  Dublin,  and  Royal  Astronomer  of  Ireland. 

$  The  linear  height  of  the  tide,  however,  is  not  quite  proportional  to  the 
tidal  force.  It  might  be  added  that  with  the  moon  at  such  a  distance,  the  terres- 
trial day  would  have  been  about  seven  hours.  This  increased  frequency  would 
increase  the  effects  of  denudation  in  three  ways:  (1)  By  the  greater  volume  of 
the  water  acting;  (2)  by  the  greater  frequency  of  its  action;  (3)  by  the  greater 
velocity  of  its  motion  during  the  rise  and  fall  of  the  tide. 


264  A    COOLING    PLANET. 

the  St.  Lawrence  River  to  Niagara  Falls — into  Lake  Erie 
and  all  the  way  round  to  Chicago.  It  would  convert  all 
New  England  into  an  archipelago.  All  the  cities  of  our 
eastern  slope  would  be  inundated.  The  great  "bore" 
would  roll  up  the  Mississippi  nearly  to  St.  Paul.  St. 
Louis,  Memphis,  Vicksburg  and  New  Orleans  would  be 
submerged.  The  greater  part  of  all  the  Gulf  states 
would,  for  a  few  hours,  be  sea-bottom.  Then  the  level  of 
the  ocean  would  rapidly  subside.  The  waters  would  be 
poured  back  from  the  continent  with  the  powers  of  a 
mighty  flood.  All  the  channel-ways  would  be  rapidly 
deepened,  and  enormous  volumes  of  sediment  would  be 
carried  out  to  sea.  Then  the  tide  would  surge  back  and 
the  vast  scouring  process  would  be  repeated.  Well  might 
the  originator  of  the  conception  claim  that  if  astronomy 
could  ever  prove  the  existence  of  such  tides  during  Pa- 
laeozoic time,  some  of  the  views  of  geologists  would  be 
"absolutely  demolished."  Sir  Charles  Lyell  argued  that 
the  events  of  Palaeozoic  time  were  produced  by  such 
agencies  as  we  now  behold  in  action.  Enormous  sedimen- 
tation took  place,  but  modern  geologic  forces  are  ade- 
quate, he  thought,  for  its  accomplishment,  if  we  give 
them  unlimited  time.  But  physical  science,  as  we  shall 
see,  does  not  allow  the  geologist  unlimited  time.  He 
must  shape  his  theories  to  a  certain  measure  of  time. 
Now  here,  exclaims  Professor  Ball,  is  the  key  to  the  whole 
matter.  The  40,000-mile  moon  set  the  tide  to  work  with 
two  hundred-fold  energy,  as  compared  with  modern  tides, 
and  all  the  sedimentation  was  accomplished  easily  within 
the  time  allotted  by  astronomy. 

But  now  the  geologist  reexamines  the  data  which 
belong  to  his  province  of  investigation.  If,  during  Palae- 
ozoic time  such  terrestrial  tides  tore  through  the  land, 
some  records  of  their  tremendous  destructiveness  must  be 
preserved.  Do  we  find  them  ?  Do  we  find  the  Palaeozoic 


TIDAL   ACTION    IN    PLANETARY    HISTORY.  265 

strata  composed  of  such  enormously  coarse  materials  as 
must  have  been  spread  over  portions  of  the  ocean's  bot- 
tom by  the  hypothetical  high  tides?  Do  we  find  the  sedi- 
ments disposed  in  that  state  of  confusion  which  must 
have  resulted  from  such  violent  movements  of  the  waters? 
We  are  compelled  to  reply  in  the  negative.  This  may 
almost  cause  a  feeling  of  regret,  since  Prof.  Ball's  theory 
is  so  ingenious,  so  beautiful  and  so  apt.  But  the  truth, 
when  we  find  it,  will  be  equally  beautiful  and  equally  apt. 
The  Palaeozoic  sediments  have  been  deposited,  for  the 
chief  part,  in  quiet  seas.  The  deep  beds  of  limestones 
and  shales  are  spread  out  in  sheets  continent-  wide,  which 
testify  unmistakably  to  placid  waters  and  slow  deposition. 
Even  the  sandstones  and  grits  give  no  evidence  of  such 
tremendous  agitations  of  sea  and  sediments  as  600-feet 
tides  would  imply.  If  such  tides  ever  existed,  it  was 
anterior  to  the  Palaeozoic  ages.* 

But  if  Professor  Ball  has  erred  in  locating  such  tides 
in  Palaeozoic  time,  it  may  only  be  an  error  of  location. 
Before  Palaeozoic  time  were  other  vast  aeons  of  duration, 
and  vast  processes  of  sedimentation,  of  which  wo  have 
but  a  dreamy  and  ill-defined  conception.  Here,  certainly, 
was  scope  enough  of  time  and  space  for  600-feet  tides  to 
carry  on  their  work.  Do  the  Eozoic  strata  afford  any 
stronger  evidence  of  so  rapid  and  violent  accumulation 
as  such  tides  would  imply?  The  response  which  they 
render  to  this  inquiry  must  still  be  regarded  as  negative. 
Their  condition,  however,  seems  to  carry  us  back  to  an 

*  Such  views  have  been  published  by  Professor  J.  S.  Xewberry.  See  Trans. 
N.  Y.  Acad.  Sci.,  Jan.,  1882;  Nature,  xxv,  337,  Feb.  16,  1882,  anc*  xxvi,  56,  May 
18,  1882.  Mr.  Darwin  himself  dissents  from  Professor  Ball's  application  of  his 
theory,  in  Nature,  xxv,  213-4.  Compare,  also,  on  this  subject,  C.  Callaway, 
Nature,  xxv,  385;  A.  Hale,  ibid.;  J.  V.  Elsden,  Nature,  xxv,  409;  Haughton, 
Proc.  Amer.  Assoc..  Montreal,  Aug.  28,  1882.  Professor  Ball  replies  to  his  critics 
in  Nature,  xxvii,  201-3,  Dec,  28,  1882.  Mr.  J.  G.'Grenfel  also  argues  that  high 
tides  would  deposit  fine  sediments  ( Nature,  xxvii,  222),  but  he  overlooks  the  in- 
land action  of  a  rushing  tidal  flood. 


266  A   COOLING    PLANET. 

age  when  greater  violence  prevailed  than  characterized 
the  subsequent  Palaeozoic  time.  It  is  easy  to  suppose  that 
the  manifest  tumult  of  Eozoic  time  was  only  the  subsi- 
dence of  a  greater  tumult  in  a  still  earlier  age.  Certainly, 
it  must  be  admitted  that  most  of  the  materials  of  the 
Eozoic  rocks  are  coarser,  and  seem  to  have  been  more 
rapidly  accumulated  than  those  of  any  later  system.  Here 
are  conglomerates  containing  rounded,  flinty  constituent 
masses,  sometimes  of  huge  dimensions.  And  the  enor- 
mous thickness  of  these  primitive  strata  exceeds  by  far 
any  thickness  known  among  later  sediments.  At  the 
same  time  we  find  vast  masses  of  crystalline  limestone 
interstratified  among  the  oldest  rocks  known  ;  and  we  are 
accustomed  to  refer  such  sediments  to  periods  of  compara- 
tive quiet.  It  is  doubtful  if  even  in  the  deep  sea  compara- 
tive quiet  could  be  said  to  reign  where  the  surface  rises 
and  sinks  600  feet  every  eight  hours.  Manifestly,  any 
high  tides  of  Eozoic  time  would  not  have  been  intermitted 
for  the  deposition  of  calcareous  materials,  to  be  after- 
ward reestablished.  On  the  whole,  the  general  aspect  of 
the  lithological  masses  of  Eozoic  time  is  such  as  might 
most  reasonably  be  ascribed  to  agencies  like  those  opera- 
tive in  sedimentation  in  modern  times.  We  must  admit, 
however,  that  they  were  generally  more  energetic,  though 
at  intervals  their  violence  subsided  to  a  state  of  limestone- 
making  repose.  The  necessary  characteristics  of  extraor- 
dinary tidal  action  are  not  distinctly  manifest  in  the  oldest 
strata  that  have  been  exposed  to  our  investigation. 

But  it  is  not  necessary,  even  yet,  to  renounce  the  con- 
ception of  primitive  high  tides.  There  is  no  evidence 
whatever  that  the  oldest  strata  ever  exposed  to  human 
study  are  the  oldest  that  ever  existed.  The  conglomer- 
ates even  of  the  Laurentian  are  but  the  ruins  of  some 
older  sedimentary  rocks.  To  what  greater  depth  sedi- 
mentary strata  extend  we  can  only  conjecture.  Perhaps 


TIDAL   ACTION   IK   PLANETARY   HISTORY.  267 

they  reach  down  to  the  zone  of  temperature  where  all 
rocks  are  at  a  molten  heat,  and  perhaps  in  a  molten  condi- 
tion. It  may  be  that  in  these  deeper  and  older  beds  would 
be  discovered  the  evidences  of  accumulation  under  the 
agency  of  tides  enormously  high.  It  is  even  conceivable, 
if  not  probable,  as  we  shall  hereafter  see,  that  a  large  por- 
tion of  the  oldest  sediments  ever  deposited  has  been  re- 
duced again  to  a  state  of  fusion,  and  that  in  these  wasted 
primitive  beds  were  impressed  the  evidences  of  high  tidal 
action. 

But  whatever  the  rocks  may  testify,  or  may  be  con- 
ceived capable  of  testifying,  the  fact  of  the  slow  recession 
of  the  moon  leads  necessarily  to  the  inference  that  the 
astronomical  condition  of  enormous  tides  must  have  ex- 
isted at  some  time  in  the  past.  If  the  ocean  was  then 
in  existence,  it  experienced  this  enormous  tidal  action,  and 
its  records  were  written  in  the  sediments  of  the  time.  If 
shores  existed  they  underwent  enormous  denudation.  If 
shores  had  not  yet  arisen,  the  shallows  of  the  universal 
ocean  must  have  been  stirred.*  If  this  proximity  of  the 
moon  had  been  greatly  reduced  before  the  ocean  accumu- 
lated, then  the  vastly  more  energetic  tidal  action  was  ex 
erted  upon  a  terrestrial  globe  of  plastic  or  molten  material. 
In  this  case  we  should  have  all  the  more  reason  to  expect 
the  formation  of  those  meridional  or  submeridional  trends 
discussed  in  other  portions  of  this  work. 

While,  however,  the  evidence  appears  to  be  slight  that 
such  tides  as  Professor  Ball  conceives  have  ever  existed 
during  the  earth's  sedimentary  history,  we  may  readily 
admit  that  Eozoic  and  Palaeozoic  tides  existed  sufficiently 

*  But  there  is,  after  all,  one  consideration  which  negatives  the  existence  of 
enormously  high  tides  since  any  process  of  sedimentation  began.  Such  tides 
could  have  existed  only  when  the  earth  had  a  rotation  so  rapid  that  its  ellip- 
ticity  of  figure  would  have  been  considerably  greater  than  at  present  But  Sir 
William  Thomson  has  shown,  as  he  thinks,  that  no  great  change  has  taken  place 
in  the  ellipticity  of  the  earth  since  solidification  began.  (Thomson  and  Tail: 
Nat.  Phil., 


268  A    COOLING    PLANET. 

high  to  operate  with  much  greater  energy  than  modern 
tides.  When  the  moon  was  48  earth-radii  distant  instead 
of  60,  as  at  present,  the  length  of  the  day,  according  to 
Darwin's  method  of  computation,  must  have  been  about 
16  hours;  and  the  tide-producing  power  must  have  been 
twice  its  present  power.  But  the"  erosive  energy  of  the 
tide  is  as  the  square  of  its  height,  or  inversely  as  the  sixth 
power  of  the  moon's  distance.*  The  energy  of  tidal 
action  would  therefore  be  doubled  by  a  diminution  of  the 
moon's  distance  by  only  one  fifth.  This  is  a  diminution 
which  may  be  conceived  to  have  existed  within  that  time 
which  on  other  grounds  we  are  at  liberty  to  ascribe  to  the 
remoteness  of  the  Eozoic  and  Palaeozoic  stages  of  terres- 
trial development;  and  the  corresponding  double  tide  is 
one  which  would  have  quadrupled  the  energy  of  tidal 
action  without  working  any  greater  confusion  in  the  order 
of  the  sediments  than  the  actual  condition  of  the  strata 
seems  to  imply.  This  consideration  enables  us  to  reduce 
Eozoic  and  Paleozoic  time  to  one-fourth  the  duration 
indicated  by  the  present  rate  of  tidal  erosion. 

Tidal  erosion,  however,  is  certainly  not  the  principal 
agency  in  the  disintegration  of  rocks  and  the  formation  of 
materials  for  sedimentary  processes,  though  the  contrary 
view  was  held  by  the  older  geologists,  and  is  still  held  by 
some.f  Atmospheric  and  fluviatile  denudation,  extend- 

*  If  d  and  d'  be  two  different  distances  of  the  moon,  and  li  and  h',  the  corre- 
sponding heights  of  the  tides,  and  E  and  E'  the  corresponding  rates  of  retarda- 
tion of  the  earth's  rotation,  then,  supposing  the  linear  height  of  the  tide  to  be 
in  the  simple  ratio  of  the  moon's  tidal  efficiency, 

h   :   h'  ::  <!'»   :   <*>,  and  A"    :   h*  ::  <*'«    :   <*•>. 
If  the  two  distances  are  60  and  48  earth-radii, 

h  :  h'  ::  (48)*   :   (60)»  =  (4)»   :    (5)>  =  1:2  nearly. 
Also,  E   :  E'  ::  A»   :  h*  =  d'»   :   d*. 

But  the  erosive  posver  of  the  oceanic  tide  results  from  the  same  friction  whicli 
acts  as  a  retarding  agency,  and  hence  the  efficiency  of  tidal  erosion  is  as  the 
square  of  the  height  of  the  tide,  or  inversely  as  the  sixth  power  of  the  distance 
of  the  tide-producing  body. 

t  Von  Richthofen:   China,  Vol.  11. 


TIDAL   ACTION    IN    PLANETARY    HISTORY.  269 

ing  over  the  entire  surfaces  of  continents,  plays  perhaps,  a 
more  important  part  than  has  generally  been  conceived. 
I  shall  cite  hereafter,  some  recent  views  concerning  the 
rate  of  denudation  of  various  hydrographic  basins.  In 
this  connection  I  desire  only  to  state  that  atmospheric,  flu- 
viatile  and  torrential  actions  must  have  been  materially 
augmented  at  the  time  when  the  moon's  distance  was  48 
earth-radii,  and  the  day  was  16  hours  long.  It  is  manifest, 
as  Mr.  G.  H.  Darwin  has  reminded  us,  that  "  on  similar 
planets  at  equal  distances  from  the  sun,  and  with  the  same 
depth  of  atmosphere,  the  linear  velocity  of  the  wind  should 
vary  as  the  linear  velocity  of  a  point  on  the  planet's 
equator."  At  the  time  when  a  terrestrial  rotation  occu- 
pied but  16  hours,  the  trades  and  anti-trades  must  have 
travelled  with  a  velocity  fifty  per  cent  greater  than  at  pres- 
ent. We  can  readily  conceive  the  probability  that  atmos- 
pheric movements  so  much  more  rapid  must  have  aug- 
mented correspondingly  the  efficiency  of  wave-action  and 
the  disintegrating  power  of  the  rains,  and  at  the  same 
time  have  greatly  increased  the  volume  of  precipitation 
and  the  frequency  of  storms.  Such  aggravated  intensity 
of  meteorological  forces  must  have  been  coincident  with 
the  superior  energy  of  tidal  erosion.  Both  causes  in  con- 
currence must,  beyond  question,  have  expedited  materi- 
ally the  geological  work  whose  records  are  preserved  in 
our  oldest  strata. 

The  subject  of  high  primitive  lunar  tides  has  been  here 
considered  in  more  especial  relation  to  the  lunar-terrestrial 
system,  because  the  data  and  the  evidences  of  such  action 
would  be  more  accessible  in  this  case.  But  the  question 
is  one  of  general  and  cosmic  significance,  and  occasion 
will  again  arise  to  refer  to  the  subject  in  connection  with 
the  present  condition  of  the  planet  Mars. 


270  A    COOLING    PLAXET. 

§7.     LIQUEFACTION  OF  WATER. 

Subsidence  of  temperature  to  the  point  where  water 
should  pass  from  the  gaseous  to  the  vaporous  condition 
must  constitute  an  epoch  of  the  utmost  significance  in 
the  early  life  of  a  planet.  That  point  on  the  earth  is 
212°  Fahr.  or  100°  C.,  at  the  level  of  the  sea.  But  it  is 
well  known  that  as  the  pressure  diminishes,  as  in  ascend- 
ing a  mountain,  the  steam  point  is  lowered,  while  an 
increase  of  pressure  raises  the  steam  point.  In  fact,  it 
has  lately  been  claimed  by  Mr.  T.  Carnelly  that  water 
may  be  subjected  to  such  pressure  that  it  not  only  does 
not  become  steam  at  212°,  but  does  not  even  become 
liquid.*  The  well  established  facts  indicate  that  on  a 
planet  of  small  mass,  and  correspondingly  low  atmospheric 
pressure,  aqueous  condensation  would  not  take  place  until 
the  temperature  had  subsided  below  the  terrestrial  stand- 
ard; while  on  a  planet  of  larger  mass  than  the  terrestrial, 
condensation  would  begin  at  a  temperature  above  the  ter- 
restrial standard. 

The  temperature  of  the  solidifying  point  also  varies 
with  the  pressure.  Professor  James  Thomson  first  con- 
cluded, on  theoretical  grounds,  that  when  a  substance  ex- 
pands in  passing  from  the  solid  to  the  liquid  state,  the 
temperature  of  liquefaction  is  raised  by  increase  of  pres- 
sure; and  when  it  contracts  in  liquefying,  as  in  the  case  of 
ice,  the  melting  point  is  lowered  by  increase  of  pressure. 
This  deduction  was  experimentally  verified  by  his  brother, 
Sir  William  Thomson, f  who  found  that  the  melting  point 

*  T.  Carnelly,  Nature,  xxii,  435,  where  he  announces  an  experiment  in  which 
solid  water  (called  "ice")  exists  at  a  burning  temperature.  See  also,  Nature, 
xxiii,  264,  288,  341,  383,  and  especially  communications  by  O.  J.  Lodge  and  J.  B. 
Hannay,  pp.  504  and  505.  Sec  finally,  Pioc.  Roy.  Soc.,  6  Jan.,  1881,  cited  in 
Amer.  Jour.  Set.,  Ill,  xxi,  385-90. 

tSir  W  Thomson,  Phil.  Mag.,  Ill,  xxxvii,  123;  Poggendoff's  Annalen,  Bd. 
Ixxxi,  S.  163.  See  also,  Trans.  Geol.  Soc.,  Glasgow,  vi,41-2.  The  following  is, 
perhaps,  the  rationale  of  the  law:  A  certain  amount  of  pressure  seems  to  be 


LIQUEFACTION    OF    WATER.  271 

of  ice  is  lowered  0°.059  C.  for  a  pressure  of  8.1  atmos- 
pheres, and  0°.129  C.  for  a  pressure  of  16.8  atmospheres. 
Mousson*,  also,  proved  that  ice  melts  at  —18°  to— 20° 
C.,  when  subjected  to  a  pressure  of  13,000  atmospheres; 
but  it  was  not  shown  that  all  this  pressure  was  neces- 
sary. Clausius  subsequently  showed,  from  theoretical 
considerations,  that  the  freezing-  point  of  water  must  be 
lowered  0°.00733  C.  for  every  atmosphere  of  increased 
pressure  —  a  result  which  agrees  with  experiment. f  Di- 
minished atmospheric  pressure  would  therefore  raise  the 
freezing  point  of  water;  and  we  might  conceive  the  pres- 
sure so  diminished  that  the  lowered  steam  point  would 
coincide  with  the  elevated  ice  point.  Under  such  circum- 
stances, water  would  present  the  same  relations  as  certain 
substances  on  our  planet  which  never  liquefy,  but  pass 
directly  from  the  solid  to  the  gaseous  state  when  heat  is 
applied.  J  On  such  a  planet  there  could  be  neither  clouds, 

requisite  to  restrain  the  molecules  of  a  solid,  within  certain  limits  of  tempera- 
•  ture,  from  relaxing  their  bonds  to  each  other;  the  same  as  a  certain  amount  of 
pressure,  within  certain  limits  of  temperature,  is  necessary  for  restraining  the 
molecules  of  the  fluid  from  flying  apart  —  the  pressure  in  all  cases  being  external. 
If  the  state  of  looser  union  requires  more  space,  increase  of  pressure  opposes 
the  change  of  state,  and  a  higher  degree  of  intermolecular  repulsion  is  required. 
Increased  heat  furnishes  this.  If  the  state  of  looser  union  requires  less  space, 
increase  of  pressure  helps  to  reduce  the  body  into  such  diminished  space,  and 
hence  less  repulsive  energy  among  the  molecules  is  required.  That  is,  the  tem- 
perature of  fusion  is  lowered.  Why  a  state  of  looser  union  requires  less  space 
(higher  density)  may  perhaps  be  explained  by  the  existence  of  larger  intermolec- 
ular intervals,  where,  as  in  ice  and  most  solids,  the  structure  is  crystalline  — 
that  is,  having  the  molecules  arranged  according  to  a  geometrical  method. 

Under  this  law  the  solidification  by  enormous  pressure  of  molten  mineral 
substances  at  temperatures  above  their  fusing  points  cannot  be  conceived  as  a 
crystalline  solidification  resulting  from  a  certain  adjustment  of  temperature  and 
pressure,  but  solidification  resulting  from  the  approximation  of  the  molecules 
under  the  same  amorphous  arrangement  as  characterizes  the  liquid.  Hence  the 
state  of  solidity  from  pressure  implies  a  higher  density  than  the  fluid  state, 
while  solidification  from  cooling  implies  a  lower  density  than  the  fluid  possesses. 

*  Mousson,  Pogg.  Annal.,  cv,  161. 

t  R.  Clansius :  Die  mechanische  Warmetheorie,  2d  ed.,  i,  173.  If  we  multiply 
0°.00733  by  8.1  and  16.8  we  get  0° .059373  and  OM23144  —  results  practically  iden- 
tical with  Sir  William  Thomson's. 

t  Compare  Clausins:  Warmetheorie,  I,  Absch.  vii,  §  6,  Uebergang  aus  dem 
Festen  in  den  luftformigen  Zustand. 


272  A    COOLING    PLANET. 

rain  nor  seas.  Water  would  be  born  out  of  steam,  in  a 
solid  snowy  state,  would  descend  like  a  shower  of  dust, 
and  rest  forever  as  rocky  material.  On  a  planet  larger 
than  the  earth,  where  liquefaction  from  aqueous  gas  or 
invisible  steam  takes  place  at  a  higher  temperature,  the 
water  must  not  only  be  hotter,  but,  under  the  higher  pres- 
sure, must  absorb  a  larger  proportion  of  gaseous  substances. 
From  both  these  causes,  meteoric  water  on  such  a  planet 
must  be  a  more  efficient  chemical  agent,  and  must  act  with 
increased  energy  on  the  rocky  substances  of  the  planet. 

As  to  substances  which  expand  in  passing  from  the 
solid  to  the  liquid  state,  only  a  few  experiments  have  been 
made.  In  fact,  there  are  very  few  substances  of  which  it 
is  certain  that  such  expansion  takes  place.  Those  experi- 
mented on  are  spermaceti,  paraffine,  stearine,  wax  and  sul- 
phur; and  it  has  been  proved  that  the  melting  point  is 
universally  raised  by  pressure.*  Sir  William  Thomson, 
as  before  stated,  inclines  to  the  opinion  that  ordinary 
rocks  belong  to  this  class;  but  I  think  I  have  cited  suffi- 
cient evidence  that  they  belong  to  the  same  class  as  water, 
and  hence  have  their  solidifying  point  lowered  by  increase 
of  pressure. 

But,  returning  to  the  inaugurative  stage  of  planetary 
hydratation,  we  can  easily  conceive  the  progressive  ad- 
vance of  water  formation  on  a  planet.  The  first  conden- 
sation would  be  revealed  by  the  filmiest  clouds  in  the 
highest  and  coolest  region  of  the  atmosphere.  On  a  planet 
of  the  mass  of  the  earth,  or  larger,  it  would  seem  proba- 
ble that  the  crust  must  still  exist  in  a  state  of  incan- 
descence, f  Such  questions  are  within  the  reach  of  mathe- 

*  Hopkins,  Report  Brit.  Assoc.,  1854,  57;  Bunsen,  Pogg.  Annal.,  Ixxxi,  562. 

t  On  the  earth  all  substances  retain  a  red  heat  till  the  temperature  falls 
below  917°  Fahr.  (J.  W.  Draper,  Amer.  Jour.  Sci.,  67,  January,  1877.)  It  is  suppos- 
able  that  though  the  crust  might  have  attained  a  dark  temperature,  the  forma- 
tion of  a  blanket  of  clouds  would  so  arrest  radiation  that  a  glowing  heat  might 
be  again  imparted  to  the  crust. 


LIQUEFACTION    OF    WATER.  273 

matics.  On  a  small  planet  condensation  would  not  begin 
until  the  surface  had  passed  the  stage  of  incandescence. 

The  accumulation  of  aqueous  vapor  in  the  higher  re- 
gions would  continue  until  the  cloudy  mass  had  settled 
through  increasing  density,  to  lower  regions.  Each  stage 
of  encroachment  on  the  lower  strata  of  the  atmosphere 
must  cost  the  clouds  volumes  of  vapor  dissipated  into  gas. 
Meantime  the  light  of  the  sun  becomes  completely  ex- 
cluded, and  the  planet  must  be  palled  in  impenetrable 
darkness,  unless  the  ignited  crust  send  its  lurid  gleam  to 
redden  the  black  vault  of  curling  and  threatening  vapors. 
Eventually  the  condensation  must  reach  such  a  point  that 
the  heat  of  the  atmosphere  can  no  longer  prevent  the  rains 
from  descending.  Ages  may  elapse  before  a  drop  can 
penetrate  to  the  planet.  Ocean  volumes  may  be  dissi- 
pated into  steam  in  mid  air  ;  but  larger  oceans  must 
return  to  the  conflict  with  the  heat.  Meantime  the  equi- 
librium of  the  electrical  forces  is  disturbed,  and  sheets  of 
lightning  glimmer  through  the  stormy  air,  and  thunders 
ever  renewed  must  jar  the  fabric  of  a  world,  and  shake  its 
watery  pall  to  ever-augmented  precipitation. 

The  forces  of  heat  in  the  progress  of  such  a  storm, 
must  undergo  increasing  wastage.  Radiation  is  more  vig- 
orous, now  that  the  cool  sheet  of  clouds  has  marshalled  its 
attacking  rains  in  closer  proximitv.  Convection  steals 
away  immense  volumes  of  heat,  as  the  stream  of  new-made 
vapors  rises  perpetually  to  the  cooler  regions.  The  crust 
at  length  glows  with  a  dimmed  ruddiness,  and  then  the 
last  ray  of  the  planet's  solar  character  expires.  The  secu- 
lar storm,  with  a  terrific  grapple  of  the  elemental  forces, 
settles  down  on  the  seething  surface,  and  holds  possession 
with  the  grim  violence  of  lightnings  and  floods.  In  this 
last  struggle  the  ocean  is  born,  and  begins  to  stretch  its 
liquid  arms  around  the  world.  It  is  a  boiling,  bubbling, 
ocean.  It  saturates  the  atmosphere  with  columns  of  pale 
18 


274  A    COOLING    PLANET. 

steam.  It  is  an  ocean  of  acid  waters.  Not  content  to 
vanquish  the  powers  of  fire  in  their  very  intrenchments, 
they  begin  to  disintegrate  and  destroy  the  rocky  substance 
of  the  intrenchments  themselves.  A  new  war  springs  into 
existence.  The  chemical  affinities  turn  their  hands  against 
each  other,  and  rapes  and  robberies  and  reprisals  make 
the  subaqueous  history  of  a  planetary  age.*  Out  of  these 
reactions  come  the  salts  which  the  sea  holds  in  solution. 
Out  of  these  reactions  come  the  earliest  precipitations  on 
the  ocean's  floor. 

The  continued  progress  of  cooling  effects,  sooner  or 
later,  the  transfer  of  the  body  of  water  from  the  atmos- 
phere to  the  planetary  surface.  Through  the  thinned 
clouds  gleams  the  sunrise  of  another  reon.  At  length 
the  exhaustion  of  the  clouds  reveals  again  the  ancient  sun, 
and  the  purified  sky,  and  the  action  of  the  planetary 
drama  now  proceeds  in  the  silent  depths  of  the  waters. 

§  8.  TRANSFORMATIONS  OP  THE  PLANETARY  CRUST. 

There  must  be  a  fire-formed  crust  on  every  planet. 
The  floor  on  which  the  first  ocean  rests  can  have  no  other 
than  an  igneous  origin.  To  tell  me  that  no  geologist  has 
ever  seen  the  earth's  primeval  crust  does  not  shake  my 
conviction  that  thus  "the  solid  earth  began."  There  are 
good  reasons  for  not  entertaining  the  expectation  of  ever 
looking  upon  any  exposure  of  the  original  fire-formed 
crust.  It  no  longer  exists.  Nor  indeed,  can  we  believe  that 
even  the  oldest  ocean-formed  rock-strata  on  our  planet  have 
been  preserved  from  destruction.  At  the  commencement 
of  sedimentation  on  any  planet,  the  crust  has  attained 
such  thickness  that  a  temporary  equilibrium  exists  be- 

*  These  chemical  reactions  in  the  primeval  history  of  the  earth  have  been 
especially  studied  hy  Dr.  T.  S.  Hunt.  Sec  his  Chemical  and  Geological  Essays. 
See  also,  an  outline  of  these  reactions  in  the  present  writer's  Sketches  of  Crea- 
tion, ch.  vi. 


TRANSFORMATIONS   OF   THE    PLANETARY    CRUST.    275 

tween  the  thermal  action  within  and  the  refrigerative 
action  without.  The  crust  presents  such  a  protection  to 
the  included  heat  that  no  further  thickening  is  demanded, 
except  as  the  mass  of  the  planet  cools.  A  thinner  crust 
would  expose  the  internal  heat  to  more  rapid  radiation, 
and  new  layers  of  crust  would  be  added  to  the  under  side. 
A  thicker  crust  would  give  the  included  thermal  forces 
the  ascendency,  and  some  layers  would  be  melted  from 
the  under  side  until  the  facility  of  thermal  conduction  and 
radiation  should  be  sufficient  to  exhaust  the  surplus  energy 
of  the  heat  within. 

Now  if,  while  such  a  crust  exists  as  equilibrates  the 
action  of  internal  and  external  forces,  a  sheet  of  oceanic 
waters  overspreads  the  surface;  still  more,  if  layers  of 
marine  sediments  become  accumulated,  the  crust  will  ex- 
perience such  a  thickening  that  the  forces  of  heat  will 
preponderate,  and  by  fusing  some  of  the  under  layers 
reduce  the  crust  to  the  equilibrating  thickness.  The  con- 
tinued accumulation  of  sedimentary  deposits  will  be  ac- 
companied by  the  continued  encroachment  of  a  fusing  heat 
upon  the  under  side  of  the  crust.*  It  is  plain  that  the 
continuance  of  these  processes  is  liable  not  only  to  remove 
and  re-fuse  totally  the  whole  thickness  of  the  fire-formed 
crust,  but  also,  any  assignable  thickness  of  the  sedimentary 
or  super-crust.  This  process  may  continue  during  the 
whole  of  the  planet's  refrig-erating  history,  though  at  no 
time  can  the  encroachment  at  the  bottom  quite  equal  the 
sedimentary  additions  at  the  surface;  since  because  the 
planet  is  necessarily  cooling  as  a  mass,  its  crust  must  ex- 
perience a  net  increase  of  thickness.  The  final  result 

*  This  idea  seems  to  have  been  first  shadowed  forth  almost  simultaneously 
by  Professor  Charles  Babbage  and  Sir  John  Herschel,  in  1836,  1837  and  1838  (see 
Ninth  Bridgewater  Treatise,  App.  G;  also  London  and  Edinb.  Phil.  Mag.,  v. 
213).  Sir  John's  suggestions  are  embodied  in  the  Ninth  Bridgewater  Treatise, 
App.  I,  in  three  letters,  dated  Feb.  and  Nov.,  1836,  and  June,  1837.  See  also 
Leonhard's  Jahrbuch,  1838,  98;  1839,  347. 


276 


A    COOLING    PLANET. 


might  be  that  sedimentary  beds,  accumulated  even  after 
the  dawn  of  the  organic  epoch,  might  come  to  occupy  the 
lowest  position.  Organic  forms  comparatively  high  might 
seem  to  begin  the  succession  of  life  by  holding  position  in 


FIG.  47. — ASCENT  OF  ISOTHERMAL  PLANES  IN  A  PLANET'S  CRUST. 

the  oldest  accessible  rocks.     Thus  the  palieontological  in- 
vestigator would  be  foiled  by  an  illusion. 

These  changes  are  illustrated  by  the  accompanying  dia- 
gram, Figure  47.     The  Hue  c  c'  represents  the  bottom  of 


TRANSFORMATIONS   OF   THE   PLANETARY   CRUST.    277 

the  sea,  on  which  sediments  are  in  process  of  accumulation. 
Under  some  circumstances  the  ocean  basin  would  thus 
undergo  a  process  of  filling1,  and  the  sea-bottom  c  c'  would 
occupy  successively  higher  positions.  This  would  be  the 
case  if  the  general  configuration  of  the  planetary  crust 
were  to  remain  unchanged,  the  material  deposited  in  the 
sea  being  only  the  amount  removed  from  the  land.  In 
most  cases,  however,  slow  wrinkling  would  be  in  progress, 
so  that  the  ocean's  bottom  would  suffer  a  gradual  subsid- 
ence. Let  us  assume  that  the  bottom  c  c'  remains  at  a 
constant  level  notwithstanding  sedimentary  accumulation, 
the  sinking  being  equal  to  the  amount  of  sedimentation. 
Then  let  c  r  or  c'  /•'  represent  the  constant  thickness  of 
crust  determined  by  the  thermal  conductivity  of  the  crust- 
materials.  A,  on  the  left,  represents  a  section  of  the  fire- 
formed  crust,  and  M,  a  portion  of  the  underlying  molten 
matter. 

Now,  if  marine  sedimentation  accumulates  the  layer  B, 
the  ocean  bottom  retaining  its  level,  a  portion  of  A  repre- 
sented by  A',  will  be  sunken  into  the  molten  mass  M,  and 
reduced  to  a  state  of  fusion.  If  another  sedimentary  layer 
C,  is  laid  down,  nearly  the  whole  of  A  may  be  sunken  and 
merged  into  the  fused  mass  M;  and  the  heat  conducted 
into  B  will  partially  obliterate  its  stratification  by  crystalli- 
zation and  other  modes  of  metamorphism.  If,  thirdly,  we 
suppose  the  layer  D  to  be  deposited  and  sunken,  the  whole 
of  A  may  now  become  merged  in  the  molten  mass,  and  a 
portion  of  B  represented  by  B'  will  suffer  the  same  fate. 
The  remainder  of  B  will  become  highly  metamorphosed, 
and  similar  action  will  extend  upward  into  C.  Evidently, 
the  same  process  may  continue  until  some  fossiliferous  for- 
mation becomes  sunken  to  the  line  r  r'. 

The  line  r  r'  marks  the  isothermal  plane  at  which  the 
temperature  is  at  the  fusing  point  of  the  rocks.  Planes  of 
lower  temperature  pass  through  the  planetary  crust  in 


278  A    COOLING    PLANET. 

positions  above  this  and  approximately  parallel  with  it. 
The  mass  M,  below,  as  before  stated,  may  be  assumed  as 
nearly  uniform  in  temperature  to  the  planetary  centre. 
The  progress  of  sedimentation  thus  appears  to  cause  a  rel- 
ative ascent  of  the  isothermal  planes  through  successively 
newer  formations  in  the  planetary  crust. 

§  9.   PLANETOGRAPHIC  EFFECTS  OF  CERTAIN  CHANGED 
ASTRONOMICAL  CONDITIONS. 

1.  Changes  in  Velocity  of  Rotation.  —  Tt  has  been 
shown  that  one  of  the  actions  of  tides  upon  a  planetary 
body  tends  to  diminish  its  rate  of  rotation.  Correspond- 
ingly, its  equatorial  protuberance  will  tend  to  diminish. 
In  the  case  of  a  planet  still  retaining  its  liquid  condition, 
the  equatorial  subsidence  will  keep  nearly  even  pace  with 
the  retardation.  To  whatever  extent  viscosity  exists,  the 
subsidence  will  follow  the  retardation.  There  will  exist 
an  excess  of  protuberance  beyond  the  equilibrium  figure 
due  to  the  actual  rotation,  and  this  will  act  as  an  additional 
retardative  cause.  In  the  case  of  an  incrusted  and  some- 
what rigid  planet,  the  excess  of  ellipticity  would  attain  its 
greatest  value.  It  would  continue  to  augment  until  the 
strain  upon  the  mass  should  become  sufficient  to  lower  the 
excessive  protuberance  to  the  equilibrium  figure.  The 
recovery  of  this  figure  might  take  place  convulsively.  The 
equatorial  regions  would  then  subside  and  the  polar  would 
rise.  In  the  case  of  an  incrusted  planet  extensively  cov- 
ered, like  the  earth,  by  a  film  of  water,  retarded  rotation 
would  be  attended  by  a  prompt  subsidence  of  the  equa- 
torial waters,  and  rise  of  the  polar  waters  to  about  twice 
the  same  extent.  In  other  words,  the  equatorial  lands 
would  emerge  and  the  polar  lands  would  become  sub- 
merged. The  amount  of  emergence  would  diminish  with 
increase  of  distance  from  the  equator,  and  the  amount  of 
submergence  would  diminish  with  increase  of  distance 


EFFECTS    OF    ASTRONOMICAL   CHANGES.  279 

from  the  pole.  In  about  the  latitude  of  30°  the  two  ten- 
dencies would  meet  and  neutralize  each  other.  Under 
these  conditions,  an  incrusted  and  ocean-covered  planet, 
since  it  must  be  undergoing  a  process  of  rotary  retarda- 
tion, must  possess  the  deepest  oceans  about  the  poles,  and 
the  shallowest  about  the  equator.  The  first  emergences 
of  land,  accordingly,  will  take  place  within  the  equatorial 
zone;  and  the  highest  elevations  and  greatest  land-areas 
will  exist  within  that  zone.  The  elevation  of  equatorial 
land  masses  would  interpose  new  obstructions  to  the  equa- 
torial ocean  current.  This  would  divert  it  in  new  direc- 
tions, and  thus  modify  all  climates  within  reach  of  oceanic 
influences.  Changes  of  currents  would  necessitate  the 
migration  of  marine  faunas,  and  changes  of  climate  would 
modify  the  faunas  and  floras  of  the  land. 

But  the  protrusion  of  the  equatorial  land-mass  could 
not  increase  indefinitely.  The  same  central  force  which 
retains  the  ocean  continually  at  the  equilibrium  figure, 
strains  the  solid  mass  in  the  same  direction.  The  strain 
must  at  length  become  greater  than  the  rigidity  of  the  mass 
can  withstand.  The  equatorial  land  protuberance  will 
subside  toward  the  level  of  the  ocean.  Some  parts  of  the 
ocean's  bottom  must  correspondingly  rise.  Naturally,  the 
parts  about  the  poles  will  rise  most.  Thus  some  equatorial 
lands  will  become  submerged  and  some  northern  and 
southern  areas  may  become  newly  emergent. 

But  these  vertical  movements  would  not  be  arrested 
precisely  at  the  point  of  recovery  of  the  equilibrium 
figure.  As  suggested  by  Professor  J.  E.  Todd*,  and  less 
explicitly  by  Sir  William  Thomson,  the  movement  would 
pass  the  equilibrium  figure  to  an  extent  proportional  to 
the  cumulation  of  strain.  The  equatorial  region  would 
become  too  much  depressed  and  the  polar  regions  too 
much  elevated.  The  effect  of  this  would  be  to  accele- 

*  Todd:    Amer.  Naturalist,  xviii,  15-26. 


280  A   COOLING   PLANET. 

rate  the  rotation  sufficiently  to  neutralize  the  ceaseless 
tidal  retardation.  The  day  would  be  shortened.  The 
ocean  would  rise  still  higher  along  the  shores  of  equa- 
torial lands,  and  subside  along  the  shores  of  polar  lands. 
An  extension  of  polar  lands  would  immediately  modify 
the  climates  of  the  higher  latitudes.  They  would  become 
subject  to  greater  extremes.  A  considerable  elevation  of 
polar  lands  would  diminish  the  mean  temperature,  and  the 
region  of  perpetual  snow  would  be  enlarged.  These  effects 
would  visit  the  northern  and  southern  hemispheres  simul- 
taneously. 

Such  effects  would  follow  from  an  excessive  subsidence 
of  equatorial  lands.  But  the  constant  retardative  action 
of  the  tides  would  cause  the  equatorial  lands  again  to 
emerge,  and  protrude  beyond  the  limits  of  the  equilibrium 
figure  attained  in  a  later  age.  Thus  the  former  conditions 
would  return,  and  the  former  events  would  be  repeated. 
In  the  nature  of  force  and  matter,  these  oscillations  should 
be  repeated  many  times.  Professor  Todd  suggests  that 
the  present  terrestrial  age  is  one  of  equatorial  land  sub- 
sidence, and  of  high  latitude  emergence.  Immediately 
preceding  the  present,  the  Champlain  epoch  was  one  of 
northern  and  probably  of  south  polar  subsidence;  while 
further  back,  in  the  Glacial  epoch,  we  have  evidence  of 
northern  and  perhaps  also  of  south  latitude  elevation.  He 
thinks  the  series  of  oscillations  may  be  traced  backward 
to  the  epoch  of  the  earliest  solid  records  of  the  earth's 
changes. 

The '  periodical  elevation  and  subsidence  of  the  equa- 
torial and  polar  regions  would  change  the  positions  of  ocean 
currents,  and  consequently  the  oceanic  temperatures  in 
given  situations  would  be  changed.  Change  of  depth 
alone  would  result  in  change  of  temperature,  since  recent 
researches  have  shown  that  the  abysses  of  our  oceans  are 
filled  with  water  possessing  a  polar  temperature,  while 


EFFECTS   OF  ASTRONOMICAL   CHANGES.  281 

shallower  seas  possess  temperatures  graduated  to  their 
depth,  and  influenced  near  the  surface  by  the  latitude. 
Changes  of  oceanic  temperature,  produced  by  either  of 
these  causes,  would  lead  to  the  extinction  or  migration  of 
faunas.  As  the  movements  here  contemplated  are  cyclical, 
the  same  conditions  would  recur  again  and  again;  and 
accordingly  the  same  fauna  might  return  again  and  again 
to  the  same  region,  with  intervals  of  occupation  by  another 
fauna.  Progressive  sedimentation  would  preserve  the 
records  of  such  faunal  alternations;  and  there  would  be 
presented  the  phenomena  of  "  colonies,"  "  reapparitions," 
and  other  faunal  dislocations  in  the  vertical  and  horizontal 
distribution  of  fossil  remains.  These  phenomena  are 
well  known  to  the  student  of  geology.*  The  progressive 
regional  differentiation  of  lands  and  seas  due  to  the  secular 
loss  of  planetary  heat  would  be  a  cumulative  cause  of  slow 
but  inevitable  changes  in  the  fauna  at  its  successive  recur- 
rences, and  would  limit  the  number  of  recurrences  of  the 
same  fauna.  This  action  would  be  most  sensibly  felt  in 
shallower  seas  and  on  land.  The  depths  of  the  ocean, 
which  retain  most  uniformly  their  cosmic  conditions,  would 
witness  the  longest  series  of  recurrences  of  the  same  or  a 
kindred  fauna. 

2.  Retarded  Orbital  Motion. —  Strong  deductive  indi- 
cations exist,  as  has  been  shown,  that  the  orbits  of  the 
planets  and  satellites  have  been  enlarged.  Not  to  speak 
of  other  causes,  this  is  one  of  the  indirect  effects  of  tidal 

*  M.  Joachim  Barrande,  Colonies  Bull.  Soc.  geol.  de  France,  xvii,  602,  1860; 
Defense  des  Colonies,  Part  1, 1861;  Part  II,  1862;  Part  III,  1865;  Part  IV,  1870; 
Part  V,  1881.  Prof.  James  Hall,  Trans.  Amer.  Phil.  Soc.,  1866,  p,  246,  in  advance  of 
Palaeontology  of  New  York,  vol.  iv,— these  views  being  repeated  at  meeting  of 
National  Academy,  Hartford,  1867,  and  indorsed  by  Prof.  L.  Agassiz;  A.  H. 
Worthen,  Proc.  A.  A.  A.  S.,  xix,  172-5, 1870,  Troy ;  but  see  Prof.  Hall's  criticisms, 
id.,  xxii,  321-35,  reprinted  in  Appendix  to  Twenty-seventh  Rep.  New  York  Regents, 
117-31 ;  Prof.  H.  S.  Williams,  On  a  Remarkable  Fauna  at  the  Base  of  the  Chtmung 
Group  in  New  York,  Amer.  Jour.  ScL,  III,  xxv,  97-104,  Feb.,  1883,  and  Note,  p. 
311 ;  but  see  S.  Calvin,  Amer.  Jour.  Set.,  Ill,  432-6. 


282  A   COOLING    PLANET. 

action.  Each  planetary  year  has,  in  the  remote  past,  been 
shorter  than  at  present.  In  the  same  proportion,  each 
season  on  each  of  the  planets  —  if  we  may  generalize  the 
term  season  in  a  qualified  sense  —  has  been  shorter.  It 
ought  not  to  be  supposed  that  the  epoch  of  sensibly  shorter 
years  has  been  so  recent  as  to  offer  an  explanation  of  the 
extreme  longevity  attributed  to  the  "antediluvians."  The 
shorter  years,  however,  must  have  been  experienced  during 
the  progress  of  the  geological  periods.  Whatever  actions 
accompany  the  transitions  from  summer  to  winter,  and 
from  winter  to  summer,  must  consequently  have  been  more 
frequently  repeated.  All  geological  effects  attributable  to 
such  actions  must  correspondingly  have  been  augmented. 
Each  round  of  the  seasons  brings  its  appropriate  precipi- 
tations, erosions  and  disintegrations;  and  when  these 
rounds  were  twice  as  frequent,  geological  changes  were 
more  rapid.  Geological  actions  were  also  more  energetic, 
in  consequence  of  the  rapidity  of  the  transition  from  one 
climatic  state  to  another.  At  the  same  time,  also,  the 
nearer  proximity  of  the  sun  would  bring  a  greater  amount 
of  solar  heat,  which  is  the  prime  mover  in  all  the  seasonal 
changes.  Shorter  years  and  shorter  seasons  imply  different 
adaptations  in  the  natures  of  animals  and  plants.  The 
processes  of  seasonal  reproduction  were  accelerated;  and 
where  the  same  work  was  done  in  less  time,  the  functional 
powers  must  have  moved  with  greater  efficiency  or  greater 
celerity. 

3.  Increase  of  Obliquity  of  Ay  is  to  Plane  of  Orbit. — 
Another  influence  of  tidal  action  inclines  the  planetary 
axis,  within  certain  limits,  at  an  increasing  angle  with  the 
axis  of  the  orbit.  The  most  obvious  consequence  of  this 
(which  is  augmented  and  diminished  by  changes  in  the 
plane  of  the  orbit  as  compared  with  an  invariable  plane) 
is  to  widen  the  torrid  and  the  frigid  zones,  and  narrow  the 
temperate  zones. 


EFFECTS   OF    ASTRONOMICAL   CHANGES.  283 

In  the  subjoined  diagram,  N  S  represents  the  axis  in 
one  state  of  inclination.  The  date  is  the  summer  solstice 
of  the  northern  hemisphere.  R  R  are  parallel  solar  rays 
whose  points  of  tangency  with  the  planet's  surface,  as  at 
P,  determine  the  position  of  the  polar  circles,  and  the 
limits  N  P  of  the  polar  zone;  O,  the  central  ray  at  this  date, 
vertical  at  T,  determines  the  position  of  the  northern 
tropic,  T  T,  and  the  breadth,  T  A,  of  the  torrid  zone,  and 
T  P,  of  the  temperate  zone. 

Now  suppose  the  inclination  to  be  increased  so  that 


FIG.  48. —  CLIMATIC  EFFECT  OF  INCREASED  OBLIQUITY  OF  A  PLANETARY  Axis. 


N'  S'  represents  the  position  of  the  axis.  Then  N'  P'  will 
represent  the  limits  of  the  polar  zone,  T  A'  the  width  of 
the  torrid  zone,  and  P'  T,  the  width  of  the  temperate  zone. 
With  an  inclination  of  45°,  the  temperate  zone,  in  the 
sense  here  explained,  would  vanish. 

The  widening  of  the  torrid  zone  would  extend  the 
range  of  products  depending  on  a  torrid  summer  climate, 
but  would  depress  the  winter  temperature  along  the  bor- 
ders of  the  zone,  since  in  winter  the  days  would  be  shorter 
and  the  meridian  sun  would  have  less  altitude.  In  other 


284  A.   COOLING    PLANET. 

words,  the  torrid  summer  would  extend  into  higher  lati- 
tudes ;  but  the  same  latitudes  would  experience  during 
winter  a  lower  depression  of  temperature  than  they  would 
with  a  less  axial  inclination.  There  would  be  a  wider 
thermal  contrast  between  the  tropical  summer  and  the 
tropical  winter  throughout  the  whole  breadth  of  the  zone. 
This  circumstance  would  react  upon  the  organic  kingdoms. 
Plants  and  animals  must  endure  greater  extremes.  Those 
most  susceptible  to  climatic  influences  might  become 
dwarfed  or  exterminated. 

The  widening  of  the  frigid  zone  implies  more  sunshine 
in  summer..  The  sun  will  attain  to  a  higher  elevation  at 
every  parallel,  and  the  area  enjoying  summer  days  without 
a  sunset  will  be  enlarged.  The  consequence  of  this  must 
be  a  more  extensive  disappearance  of  snow  and  ice,  accu- 
mulated on  planets  with  snow-capped  poles  during  the 
previous  winter.  On  the  contrary,  the  increased  inclina- 
tion extends  the  area  deprived  of  the  sun  in  winter,  but  it 
does  not  increase  the  severity  of  the  cold  ;  since  when  the 
sun  is  a  great  distance  below  the  horizon  his  influence  is 
no  less  felt  than  when  but  a  short  distance  below.  The 
winter  season  would  therefore  not  tend  materially  to  aug- 
ment snowy  accumulations  beyond  the  amount  resulting 
from  a  low  axial  inclination.  The  combined  result  of 
summer  and  winter  would  be,  in  this  view,  a  diminished 
amount  of  snow  and  ice.  Correspondingly,  a  diminished 
inclination  of  the  axis  would  result  in  an  increased  amount 
of  snow  and  ice,  though  the  area  covered  would  be  less. 
These  consequences  would  be  simultaneous  in  the  two 
polar  zones. 

With  no  inclination  the  sun  would  be  perpetually  in 
the  horizon  of  either  pole.  A  temperature  nearly  that  of 
external  space  would  prevail  uninterruptedly.  But  at  no 
great  distance  from  the  pole,  perpetual  sunshine,  though 
from  a  slanting  sun,  would  tend  greatly  to  the  dissolution 


EFFECTS    OF    ASTRONOMICAL   CHANGES.  285 

of  snowy  accumulations.  At  26°  from  the  pole  the  alti- 
tude of  the  sun  would  be  about  the  same  as  the  midday 
sun  at  New  York  at  the  end  of  December.  But  it  would 
remain  permanently  at  that  altitude.  It  is  doubtful 
whether  this  position  of  the  sun  would  be  compatible  with 
a  snow  cap  extending  lower  than  26°  from  the  pole.  A 
slight  inclination  would  throw  an  area  about  the  pole 
into  a  state  of  sunlessness  during  a  portion  of  the  winter, 
but  it  would  gain  in  altitude  of  sun  during  the  summer. 
On  the  whole,  it  seems  very  doubtful  whether  anv  inclina- 
tion, great  or  small,  would  create  the  conditions  for  a 
permanent  ice  cap  reaching  as  far  as  the  latitude  of  40°.* 
4.  Change  in  Relative  Positions  of  Apsides  and  Equi- 
noxes.— The  precession  of  the  equinoxes  arises  from  a  slow 
gyratory  motion  of  the  axis  of  the  planet,  causing  each 
pole  to  describe  a  somewhat  regular  circle.  This  results 
from  the  action  of  the  sun  upon  the  equatorial  protuber- 
ance, joined  to  the  resultant  of  the  combined  actions  of 
the  satellites,  when  they  exist.  The  rate  and  amount  of 
the  disturbance  is  therefore  connected,  among  other  things, 
with  the  amount  of  the  protuberance  and  the  amount  of 
the  inclination.  The  effect  of  this  change  is  to  cause  the 
planetary  axis  to  be  inclined,  at  different  periods,  in  differ- 
ent absolute  directions  ;  and  the  total  movement  relative 
to  a  point  in  the  planet's  orbit  is  also  affected  by  a  motion 
of  the  apsides.  In  the  case  of  all  the  planets  except 
Venus  (and  possibly  Neptune)  the  apsidal  motion  is 
direct,  and  therefore  diminishes  the  effect  of  precession. 
In  the  case  of  the  earth  the  equinoctial  point  falls  back 
50".  1  annually.  It  would  of  itself,  therefore,  complete 
the  circuit  of  the  ecliptic  in  twenty-five  thousand,  eight 
hundred  and  sixty-eight  years.  But  as  the  apsis  goes  for- 

*The  reader  will  find  some  discussions  of  axial  inclination  as  a  cause  of 
terrestrial  glaciation  in  Drayson.  Qi/ar.  Jour.  Geol.  Soc..  xxii ;  Thomas  Belt, 
Id.,  Oct.,  1874,  abstract,  Amer.  Jour.  Sri.,  Ill,  ix,  313-5:  Croll:  Climate  and 
Time,  ch.  xxv,  where  Drayson  and  Belt  are  discussed. 


286  A    COOLIXG    PLANET. 

ward  to  meet  it  at  the  rate  of  11". 24*  annually,  this 
would  complete  a  revolution  in  one  hundred  and  fifteen 
thousand,  three  hundred  and  two  years.  The  approxima- 
tion of  the  equinox  and  the  apsis  is  the  sum  of  these 
motions,  61". 34,  and  hence  the  equinox  returns  to  the 
same  position  in  relation  to  the  apse  in  twenty-one  thou- 
sand, one  hundred  and  twenty-eight  years.  The  earth's 
axis  was  inclined  exactly  from  the  sun  at  perihelion,  in  the 
year  1248.  It  now  (1883)  consequently  points  10°  49'  11" 
back  (or  west)  of  perihelion,  so  that  perihelion  is  reached 
about  ten  days  after  the  winter  solstice. 

It  results  from  these  two  secular  movements  that  at  a 
certain  time,  the  planetary  axis  will  lean  toward  the  sun 
when  at  the  aphelion  point ;  at  another,  toward  the  sun 
when  at  the  perihelion  point.  In  the  former  case,  summer 
occurs  in  the  northern  hemisphere  during-  aphelion,  and 
winter  during  perihelion.  In  the  latter  case,  summer 
occurs  in  the  northern  hemisphere  during  perihelion,  and 
winter  during  aphelion.  The  terms,  of  course,  are  in- 
verted in  reference  to  the  hemisphere  below  the  plane  of 
the  planet's  orbit. 

In  the  accompanying  figure,  let  N  S  represent  the  axis 
of  a  planet  from  such  a  point  of  view  that  equator,  trop- 
ical and  polar  circles  are  projected  in  right  lines.  Let  the 
position  of  the  planet  be  perihelion,  with  the  solar  rays 
R,  C,  R,  coming  from  the  right.  The  north  pole  leans 
toward  the  sun.  Summer  in  the  northern  hemisphere  and 
winter  in  the  southern,  occurs  during'  perihelion.  Next, 
suppose,  in  the  same  diagram,  the  north  pole  is  turned 
away  from  the  sun  at  perihelion,  and  the  solar  rays 
R',  C',  R',  come  from  the  left.  Now,  winter  in  the  north- 
ern hemisphere  and  summer  in  the  southern,  occurs  during 
perihelion. 

*The  value?  of  these  variations  are  taken  from  the  Encyclopedia  Britan- 
nica,  Art.  Astronomy. 


EFFECTS   OF    ASTRONOMICAL   CHANGES.  287 

-R 


FIG.  49.    CLIMATIC  EFFECT  OF  CHANGES  is  RELATIVE  POSITIONS  OF  APSIDES 
AND  SOLSTICES. 


The  planetary  effect  of  such  changes  in  the  position  of 
the  axis  during  the  summer  and  winter  periods  of  each 
hemisphere,  would  be  climatic.  In  the  first  case  supposed, 
summer  in  the  northern  hemisphere  concurs  with  the 
planet's  greatest  proximity  to  the  sun.  The  solar  action 
on  the  polar  snow  and  ice,  if  they  exist,  would  be  greater 
than  when  summer  occurs  in  aphelion,  nearly  in  the  ratio 
of  the  square  of  the  perihelion  and  aphelion  distances. 
In  other  words,  the  summer  warmth  would  show  greatest 
excess  in  planets  having  orbits  of  highest  eccentricity; 
though  the  effect  of  superior  eccentricity  would  be  dimin- 
ished with  increase  of  mean  distance  from  the  sun,  and 
increased  with  diminution  of  mean  distance.  The  concur- 
rence of  the  summer  solstice  with  perihelion  would  there- 
fore tend  to  diminish  polar  glaciation.  During  the 
aphelion  winter,  the  solar  action  would  be  diminished, 
below  the  solar  intensity  during  a  perihelion  winter,  at  all 
points  having  the  sun  above  the  horizon ;  but  not  sensibly 
changed  at  points  having  the  sun  below  the  horizon.  The 
resultant  effect  throughout  the  polar  zone  would  probably 
be  some  increase  of  glaciation.  This  winter  increase  of 


288  A    COOLING    PLANET. 

glaciation  would  go  far  to  neutralize  the  summer  diminu- 
tion. Professor  James  Croll  is  of  the  opinion  that  in  the 
case  of  the  earth,  it  would  entirely  neutralize  it;  so  that 
the  movement  of  the  equinox  would  never  result  in  any 
change  in  polar  glaciation.*  On  the  contrary,  MM.  Ad- 
he'marf  and  Julien  J  and  Mr.  J.  J.  Murphy  §  maintain  that 
the  coincidence  of  the  summer  solstice  with  perihelion, 
and  the  winter  solstice  with  aphelion  would  decidedly  in- 
crease northern  g'laciation.  The  converse  of  this  relation 
existed,  in  the  case  of  the  earth,  in  the  year  1248,  and 
these  authors  maintain,  by  means  of  numerous  citations, 
that  the  winter  climate  of  Europe  was  milder  at  that 
epoch  than  at  present.  The  passage  of  the  winter  solsti- 
tial point  ten  or  twelve  degrees  before  the  perihelion 
point  already  results,  they  say,  in  a  perceptible  increase 
of  wintry  cold.  It  is,  however,  scarcely  credible  that  so 
trifling  an  increase  of  distance  from  the  sun  at  the  winter 
solstice  should  result  in  any  perceptible  change  in  the 
winter  climate;  or  that  the  whole  difference  between 
perihelion  and  aphelion  should  ever  cause  such  general 
glaciation  of  the  northern  continents  as  seems  to  have 
existed  in  a  former  geological  period.  This  doubt  may 
well  be  based  on  the  summer  influence  of  conjunction  of 
summer  solstice  and  perihelion.  We  are  not  in  a  posi- 
tion, therefore,  to  conclude  that  changes  in  the  angle 
made  by  the  line  of  equinoxes  with  the  line  of  the  apsides 
would  cause  any  important  residual  effects  upon  planetary 
climate. 

5.  Changes  of  Orbital  Eccentricity. — The  immediate 
effect  of  increased  eccentricity  is  to  increase  the  differ- 

*  Croll:  Climate  and  Time,  &3;  Phil.  Mag.,  Sept.,  1869.  On  this  subject,  sec 
also  Arago,  Annuaire,  1834,  and  Edinb.  New  Phil.  Jour.,  vi,  1834. 

t  Adhemar:  Revolutions  de  la  mer,  2d  ed.,  1860. 

i  Julien :  Courants  et  revolutions  de  V atmosphere  et  de  la  mer.  See  also,  Lc 
Hon:  L' Homme  J'ossile  en  Europe,  4ine.  ed.,  1877,  Seconde  Partie. 

§  Murphy,  Quar.  Jour.  Geol.  Soc.,  xxv,  350. 


EFFECTS   OF   ASTKONOMICAL   CHANGES.  289 

ence  between  the  perihelion  and  aphelion  distances  of  the 
planet.  Whatever  climatic  or  other  consequences  proceed 
from  this  difference  will  be  exaggerated  by  increased 
eccentricity.  But  the  nature  of  the  climatic  effect  will 
depend  on  the  angle  of  the  equinoctial  line  with  the 
apsidal  line,  and  also,  whether  a  particular  solstice  occurs 
on  the  perihelion  or  the  aphelion  side  of  the  equinoctial 
line.  Let  us  suppose  that  the  summer  solstice  of  the 
northern  hemisphere  coincides  with  perihelion.  Thus, 
with  increased  eccentricity,  the  perihelion  distance  in 
summer  is  less,  and  the  summer,  though  shorter,  is 
warmer;  also  the  aphelion  distance  in  winter  is  greater, 
and  the  winter  is  longer  and  colder.  The  winter  will 
therefore  accumulate  more  snow  and  ice,  and  the  snow 
cap  will  extend  to  a  lower  latitude.  But  then  this  accu- 
mulation will  be  acted  on  by  the  increased  summer  heat. 
If,  therefore,  the  accumulation  is  not  sufficient  to  with- 
stand this  increased  heat,  no  residual  effect  will  remain. 
If  any  part  of  the  accumulation  is  sufficient  to  continue 
through  the  hot  summer  there  will  be  a  secular  accumula- 
tion of  northern  snow  and  ice.  But  it  must  be  mentioned 
that  the  solvent  effect  of  the  hot  summer  will  not  be  pro- 
portional to  the  perihelion  distance.  The  solar  rays,  fall- 
ing on  surfaces  of  snow  and  ice,  will  be  exhausted  first 
in  the  formation  of  vapor,  which  will  obstruct  the  access 
of  solar  heat,  and  neutralize,  to  a  large  extent,  the  excess 
of  summer  warmth.  The  effective  solvent  force  of  the 
solar  rays  may  not,  therefore,  much  exceed  their  force  at 
the  aphelion  distance,  and  there  must  remain  a  residual 
increase  of  northern  glaciation.  This,  at  least,  is  the  view 
taken  by  Croll.*  It  does  not  appear,  however,  that  the 
residual  increase  can  ever  amount,  upon  the  'earth,  to  "a 
reign  of  ice,"  such  as  prevailed  in  the  Quarternary  period 

*Croll:  Glimate  and  Time, 
19 


290  A    COOLIXG    PLANET. 

% 

of  geology.*  Mr.  Croll  himself  does  not  maintain  this; 
but  he  argues  that  in  the  case  of  the  earth,  the  configura- 
tion of  the  continents  has  been  such  as  to  direct  the  equi- 
noctial current,  during  the  period  of  summer  perihelion, 
away  from  the  northern  hemisphere,  and  thus  indirectly  to 
induce  the  conditions  of  a  "reign  of  ice."f 

It  is  manifest  that  the  production  of  a  state  of  north- 
ern glaciation  by  the  concurrence  of  high  eccentricity  and 
a  perihelion  summer  solstice  would  be  attended  by  recip- 
rocal conditions  of  climate  in  the  southern  hemisphere; 
and  that  all  these  conditions  would  be  reversed  by  low 
eccentricity  and  an  aphelion  summer  solstice.  It  is  also 
manifest  that  each  astronomical  movement  would  produce 
a  climatic  cycle  of  its  own  —  that  connected  with  the 
eccentricity  having  a  variable  period  of  some  tens  or  hun- 
dreds of  thousands,  and  that  connected  with  precession 
and  the  movement  of  the  apsides  having  a  period  of  about 
21,000  years.  When  the  effects  from  the  two  causes 
concur,  a  maximum  climatic  effect  would  result;  when  they 
conflict,  a  minimum. 

*  Sir  J.  Herschel,  On  the  Astronomical  Causes  ivfiich  may  Influence  Geologi- 
cal Phenomena,  Geological  Transactions,  1832;  Treatise  on  Astronomy,  §  315; 
Outlines  of  Astronomy,  §  368;  Arago,  Anxuaire,  1834,  p.  199;  Edinb.  New  Phil. 
Jour.,  vi,  April,  1834,  244;  Ilumboldt:  Cosmos,  iv,  459,  Doha's  ed  ;  Phys.  De- 
scrip.  Heaven*,  336. 

t  Croll:  Climate  and  Time  ;  A.  Winchell:  Sparks  from  a  Geologist's  Ham- 
mer, 175  9i».  See  criticisms  of  droll's  theory  by  S.  Ts'ewcomb,  Ainer.  Jour.  Set., 
III.  xi,  263;  J.  J.  Murphy,  Ainer.  Jour.  Geol.  Soc.,  xxv,  350, 186ft,  abstract  Amer. 
Jour.  Sci.,  Ill,  xlix,  115-18;  Charles  Martins,  Revue  des  Deux  Mondes.  1867;  W. 
J.  MrCi-f,  Popular  Science  Monthly,  xvi,  810,  but  with  general  endorsement;  C. 
B.  Warring:  Penn.  Monthly,  1880.  Further  on  this  subject  the  reader  may  con- 
sult Lellon:  L'llomme  fossile,  pt.  ii;  Col.  Drayson,  Phil.  Mag.,  1871,  abstracted 
in  Amer.  Jour.  Sci.,  Ill,  ii,  301;  Sir  William  Thomson:  Geological  Climate, 
Trans  Geol.  Soc.,  Glasgow,  Feb.,  1877,  vol.  v,  pt.  ii;  James  Geikie:  Prehistoric 
Europe,  1880;  G.  Pilar:  Utber  die  Ursache  der  Eiszeiten;  Hirsch,  Sur  les  causes 
cosmiques  d<8  changemtnts  de  climat.  Bull,  dc  la  Societe  des  sci.,  nat.  de  Ncuf- 
chatel.  Also,  discussions  by  Croll,  Heath.  Moore  and  Pratt  in  the  Philosophical 
Magazine,  1864,  1865.  1866;  A.  R.  Wallace:  Island  Life.  W.  J.  McGee  has  very 
recently  vindicated  the  "  eccentricity  theory''  in  Amer.  Jour.  Sci.,  Ill,  xxvi.  113- 
20,  Aug.,  1883. 


OROGEXIC    FORCES.  291 

§  10.   OROGENIC  FORCES. 

The  inequalities  in  the  contour  of  the  terrestrial  sur- 
face are  scarcely  more  familiar  than  the  orographic  phe- 
nomena which  diversify  the  visible  face  of  the  moon  with 
their  lights  and  shades.  The  earth  and  the  moon  are 
equally  well  known  to  be  marked  by  mountains,  valleys 
and  plains.  The  lights  and  shades  of  the  disc  of  Mars  are 
also  generally  received  as  evidences  of  analogous  topo- 
graphical configurations.  In  general,  we  might  be  led  to 
believe  from  the  study  of  terrestrial  inequalities,  and  the 
terrestrial  forces  which  seem  adequate  to  develop  moun- 
tain features,  that  the  production  of  mountains  is  a  com- 
mon incident  in  planetary  history.  We  can  understand, 
at  least,  certain  modes  of  action  which  tend  toward  moun- 
tain development;  and  even  if  no  complete  and  satisfac- 
tory theory  can  yet  be  framed,  it  may  be  gratifying  to  the 
reader  to  learn  what  views  have  been  entertained,  and 
what  is  the  present  state  of  speculation  on  the  subject. 

In  discussing  the  origin  of  mountains,  and  of  terrestrial 
mountains  in  particular,  it  is  necessary,  first  of  all,  to  dis- 
criminate mountains  of  elevation  from  mountains  of 
relief.  The  former  are  eminences  which  have  been  mani- 
festly upraised  above  the  general  level  of  the  earth's  sur- 
face. The  latter  are  saliences  resulting  from  the  erosion 
and  removal  of  surrounding  masses.  The  interpretation 
of  erosive  phenomena  is  something  so  simple  that  the  ex- 
planation of  mountains  of  erosion  has  given  rise  to  little  dis- 
cussion. In  almost  every  case,  however,  a  mountain  mass 
inaugurated  by  actual  elevation  has  been  greatly  modified 
by  much  later  erosions.  In  many  instances,  indeed,  ero- 
sion has  completely  transformed  the  configuration  of  the 
original  upheaval,  and  it  has  sometimes  so  disguised  the 
results  of  upheaval  as  to  require  careful  study  to  discrimi- 
nate certainly  the  work  which  ought  to  be  ascribed  to 


292  A    COOLIXG    PLANET. 

elevatory  action.  But  in  this  connection  we  disregard  en- 
tirely the  sculpturing  which  has  been  performed  on  the 
surface,  and  direct  our  inquiries  to  the  nature  of  those  more 
concealed  agencies  which  seem  to  have  exerted  themselves 
somewhere  within  the  solid  crust  of  the  planet. 

Movements  of  the  earth's  solid  surface  have  been  so 
often  associated  with  volcanic  phenomena  that  it  is  natu- 
ral that  mankind  from  time  immemorial  should  have 
ascribed  mountain  formation  to  the  agency  of  internal  heat. 
The  formation  of  mountains  was,  by  the  older  geologists, 
considered  explained  by  theories  proposed  to  account  for 
the  phenomena  of  vulcanism;  and  there  is  unquestionably 
a  close  analogy  between  the  seismic  movements  which 
often  accompany  vulcanic  exhibitions,  and  the  larger  pro- 
cesses which  have  resulted  in  permanent  mountain  uplifts. 
Still,  a  slight  consideration  of  the  facts  shows  that  the 
vast  and  systematic  orographic  convolutions  of  the  terres- 
trial crust  must  have  been  produced  by  forces  widely  dif- 
ferent in  power  and  mode  of  action  from  the  disturbing 
influences  which  result  from  igneous  activities.  There  is 
reason,  indeed,  to  consider  whether  these  igneous  manifes- 
tations are  not,  conversely,  the  result  of  movements  in 
the  earth's  crust ;  and  this  is  a  question  to  which  we  will 
return  in  connection  with  molten  conditions  and  melting 
forces  upon  our  planet. 

We  will  now  proceed  to  give  a  concise  exposition  of 
the  principal  theories  which  have  been  promulgated  re- 
specting the  origin  of  mountains. 

1.  Theory  of  Upheaval  by  Aeriform  Agents. —  The 
idea  that  mountains  have  been  uplifted,  and  terrestrial  dis- 
turbances produced  by  steam,  gases,  or  other  heated  agents, 
is  as  old  as  Strabo,*  and  may  even  be  traced  to  Anaxa- 
goras,f  who  taught  that  earthquakes  are  "produced  by  the 

*  Strabo:  Geographia,  lib.  vi. 

t  Diogenes  Lagrtius :  Lives  of  (he  Most  Illustrious  Philosophers  of .  1  nt'nj >iity. 


OROGEHIC   FORCES.  293 

air  which  finds  its  way  into  the  earth."  An  attempt  was 
made  to  explain  the  origin  of  such  mountain-raising  agents, 
when  Sir  Humphrey  Davy  and  others  made  appeal  to 
chemical  action  as  a  source  of  heat,  steam  and  gases.  Sir 
Humphrey's  arguments  and  experiments  were  in  line  with 
the  current  of  new  conceptions  then  flowing  out  of  the 
new  discoveries  in  chemistry,  and  for  a  time  appeared 
extremely  plausible.  They  were  espoused  by  the  dis- 
tinguished geologist  Daubeney,  and  for  some  years  they 
commanded  very  general  credence.  Reflection,  however, 
produced  the  conviction  that  the  cause  was  insufficient  in 
generality,  endurance  and  efficiency.  Gas  and  steam-pro- 
duction through  chemical  action  has  not  probably  existed 
on  a  scale  sufficiently  vast  to  account  for  mountain-ranges 
thousands  of  miles  in  length  and  thousands  of  feet  in 
height.  And  whatever  the  magnitude  of  gas  or  steam 
production,  the  causes  operative  have  not  probably  been 
sustained  through  periods  sufficiently  prolonged.  Such 
causes  are  seen  to  be  operative  in  our  times  no  longer;  as 
they  seem  to  have  ceased  to  exist,  there  is  no  ground  for 
affirming  that  they  ever  continued  in  action  —  if  they  ever 
existed  —  for  such  length  of  time  as  is  required  by  a  his- 
tory of  mountain  development  stretching  over  a?ons  of 
geological  time.  It  is  conceivable,  indeed,  that  agencies 
of  this  kind  have  had  the  requisite  persistence,  but  the 
general  condition  of  our  planet  has  remained  compara- 
tively unchanged  through  so  many  ages,  while  the  evolu- 
tion of  mountains  has  continued,  that  very  little  probability 
exists  that  the  equilibrium  of  the  chemical  forces  had  not 
been  attained  during  the  Archaean  ages.  But  a  further 
and  more  fatal  objection  to  the  present  theory  arises  from 
the  inadequacy  of  aeriform  agents  to  do  the  work  required. 
If  mountains  have  been  uplifted  by  steam  or  gases,  those 
agents  must  have  borne  the  weight  of  the  mountains  and 
overcome  the  resistances  to  motion  presented  by  the  rigidity 


294  A   COOLING    PLANET. 

of  the  rocks.  This  action  has  been  necessary,  not  only  to 
uplift  the  mountains,  but  to  maintain  them.  Now,  this 
work  demands  both  improbable  persistence  and  impossible 
energy.  The  steadiness  of  mountains  is  not  maintained 
upon  reservoirs  of  wind.  Nor  have  gases  or  steam  the 
unlimited  power  of  reaction,  even  at  the  highest  tem- 
peratures, which  is  implied  in  bearing  the  weight  of 
the  Andes  or  Himalayas.  Such  weights  would  crush 
them  into  fluid,  viscid,  and  practically  solid  states.* 
These  objections  apply  to  the  agency  of  the  aeriform 
condition  of  matter  however  produced.  Steam  origi- 
nating from  the  penetration  of  surface  waters  to  an 
assumed  heated  interior  must  be  characterized  by  all  the 
inadequacy  of  gases  chemically  originated.  While,  there- 
fore, the  power  of  confined  steam  and  compressed  gases 
is  immense,  and  may  even  contribute  something  to  the 
phenomena  of  earthquakes,  their  elasticity  is  undoubt- 
edly limited  far  within  the  requirements  of  mountain 
formation. 

2.  Theory  of  a  Molten  Nucleus  and  a  Wrinkling 
Crust. — If  the  primitive  history  of  the  matter  of  our  planet 
has  been  such  as  set  forth  in  the  preceding  portion  of  this 
work,  there  must  have  been  a  time  when  incrustation  be- 
gan, and  there  must  have  been  a  time  when  matter  in  the 
liquid  condition  interposed  a  continuous  zone  between  the 

*  Compare  Suess:  Die  Entstehung  der  Alpen,  Wien,  1875,  abstract  in  Ainer. 
Jour.  Sci.,  Ill,  x,  446-51 ;  Dana:  Manual  of  Geology,  third  edition,  747;  Nature, 
xxi,  177,  Dec.  25, 1879;  J.  D.  Whitney,  North,  American  Review,  cxiii,  255.  It 
was  shown  by  Bischof  in  1839,  that  "  the  elastic  force  of  steam  cannot  surpass  a 
certain  maximum,  which  it  reaches  when  its  density  is  equal  to  that  of  water;" 
and  it  has  been  calculated  that  this  force  would  not  in  any  case  raise  more  than  a 
column  of  lava  seventeen  miles  high.  The  lacolitic  mountains  of  Colorado  are 
cases  in  which  a  moderate-sized  mountain  uplift  seems  In  have  been  produced 
by  the  upward  pressure  of  fluid  hypogene  matter;  and  this  is  the  nearest  approach 
known  to  mountain-making  by  a  method  of  upburst.  But  these  mountains  are 
comparatively  insignificant  in  dimensions,  and  there  is  no  evidence  of  the  inter- 
vention of  the  elastic  force  of  vapors  in  their  formation.  (See  G.  K.  Gilbert: 
Geology  of  the  Henry  Mountains,  Powell  Survey,  1877,  Nature,  xxi,  177.) 


OROGEN/IC    FORCES.  295 

solidifying  crust  and  the  consolidated  nucleus.*  This  was 
a  time,  too,  when,  according  to  the  views  entertained  of 
nebular  theory,  the  earth's  rotation  must  have  been  much 
more  rapid  than  at  present,  and  the  equatorial  protuber- 
ance much  greater.  Thus,  at  the  same  epoch,  the  freedom 
of  the  protuberance  to  slip  under  the  influence  of  nuta- 
tional  and  precessional  forces,  and  the  condition  of  greater 
efficiency  in  the  action  of  those  forces,  were  much  more 
marked  than  in  subsequent  epochs,  when  the  earth's  mass 
became  bodily  rigid,  and  the  oblateness  was  diminished. 
But  passing  by  the  possible  climatic  consequences  of  a 
shifting  of  the  terrestrial  crust  in  relation  to  the  axis  of 
rotation,  I  wish  only  to  indicate  here  the  grounds  of  the 
theory  that  the  simple  process  of  cooling  may  have  devel- 
oped surface  rugosities  which  grew  into  mountain  magni- 
tude. 

The  conception  of  wrinkling  as  an  incident  of  terres- 
trial cooling  seems  to  have  been  entertained  by  Descartes,  f 
and  was  somewhat  definitely  enunciated  by  James  Hall  of 
Edinburgh,  in  1812,1  M.  Elie  de  Beaumont,  §  Prof.  Sedg- 

*  Prof.  James  Hall  says,  nevertheless,  that  of  the  central  mass  of  molten 
matter  "  we  know  nothing  "  (Palceont.  New  York,  III.) 

In  a  New  York  lecture  of  later  date,  before  the  American  Institute,  on  the 
Evolution  of  the  Atneiican  Continent,  he  is  reported  to  have  said :  "I  desire  to 
impress  upon  you  this  one  truth,  that  we  have  not,  in  our  geological  investigation, 
succeeded  in  going  back  one  step  beyond  the  existence  of  water  and  stratifica- 
tion— one  step  toward  this  so-called  primary  nucleus  of  molten  matter.  *  *  * 
This  original  nucleus  that  has  been  talked  about  in  geology  hag  produced  no 
effect  upon  the  surface  of  tJie  earth  ;  neither  upon  its  mountain  chains  or  any 
other  of  the  great  features  of  the  continent.  (Report  in  New  York  Tribune.) 

t  Descartes:  Principes  de  la  Philosophie,  pt.  iv,  §§41,  42,  1644.  Descartes 
gives  several  illustrative  figures,  in  one  of  which  strata  arc  shown  uplifted  and 
broken  in  a  curtain  place,  while  on  each  side  they  are  shown  depressed. 

J  James  Hall,  Trans.  Roy.  Soc.,  Edinburgh,  vii,  79, 1815,  read,  1812. 

§De  Beaumont:  Les  Systimes  de  Montagnes.  Successive  mountain  up- 
heavals, in  systems  having  each  its  own  parallelism,  "  cannot  be  referred  to 
ordinary  volcanic  forces,  but  may  depend  on  the  secular  refrigeration  of  onr 
planet.1'  (Ann.  des  Sci.  Nat.,  Sep.,  Nov.  et  Dec.,  1820;  Revue  Francaise,  No.  16, 
May,  1830;  Bui.  de  la  Soc.  giol.  de  France,  iv,  864,  May,  1847.) 


296  A    COOLIKG    PLANET. 

wick,*  M.  Constant  Prevost,f  and  William  Hopkins  ;J  but 
the  most  effective  scientific  support  of  this  doctrine  has 
been  traced  out  by  more  recent  writers.  The  starting 
point  of  the  theory  is  in  the  unequal  rate  of  cooling  of 
the  superficial  and  deeply  seated  portions  of  the  earth,  and 
further,  the  unequal  contraction  of  differently  heated 
bodies  when  cooling  from  different  temperatures.  Physi- 
cal considerations  have  shown  that  some  time  after  incrus- 
tation of  a  planet  has  begun,  the  rate  of  cooling  at  the 
surface  will  be  somewhat  slower  than  at  some  point  beneath 
the  surface,  and  that  the  surface  may  even  retain  a  con- 
stant temperature,  while  the  interior  cools.§  Mr.  G.  H. 
Darwin  has  recently  shown  that  the  actual  seat  of  most 
rapid  cooling  in  the  earth  is  probably  about  100  miles 
below  the  surface,  and  that  this  point  continues  to  descend 
as  cooling  progresses.  |  It  is  also  well  known  that  the 
rate  of  contraction  of  a  more  highly  heated  body  is  more 
rapid  than  that  of  a  body  of  lower  temperature,  when 
both  cool  the  same  number  of  degrees.  Now,  for  both 
these  reasons,  the  contraction  of  the  interior  of  the  earth 
must  be  more  rapid  than  that  of  the  cooler  and  less  rapidly 

*Sedgwick,  Trans.  Oeol.  Soc.,  Lend.,  Jan.  5,  1831,  in  a  paper  on  the  struc- 
ture of  the  Cumbrian  Mountains. 

tC.  Provost,  Sur  la  Thtorie  des  Soul'evemenls ,  Bui.  Soc.  geol.  de  France, 
xi,  183, 1840,  but  taking  a  different  view  from  de  Beaumont.  He  ascribes  the 
formatiou  of  mountains  to  "  tangential  pressures  propagated  through  a  solid 
crust,  *  *  *  and  produced  by  the  relative  rate  of  contraction  of  the  nucleus 
and  of  the  crust." 

+  W.  Hopkins,  Address  before  the  Oeol.  Soc.  of  Lond.,  1853,  Geol.  Jour.,  ix, 
Ixxxix. 

§  Maxwell :  Tlieory  of  Heat,  247 ;  Sir  W.  Thomson,  Trans.  Roy.  Soc.,  Edinb., 
1862;  Thomson  and  Tail:  Nat.  Phil.,  App.  D.  See  an  illustration  of  this  prin- 
ciple by  Rev.  O.  Fisher  in  Nat,ure,  xix,  173.  M.  Elie  de  Beaumont,  applying 
Arago's  observations  on  thermometers  placed  at  various  depths  beneath  the  sur- 
face, to  Poisson's  formulas  embodying  the  mathematical  theory  of  heat,  calcu- 
lated that  the  epoch  at  which  the  cooling  of  the  nucleus  began  lo  exceed  that  of 
the  crust  was  38,359  years  after  the  commencement  of  incrustation.  Hence  it 
might  be  inferred  that  this  epoch  determines  the  date  of  the  commencement  of 
the  process  of  wrinkling. 

II  G.  H.  Darwin,  Nature,  xix,  313,  Feb.  6,  1879. 


OROGENIC   FORCES.  297 

cooling  exterior  layers.  If,  therefore,  the  exterior  layers 
were  perfectly  rigid  and  infrangible,  the  interior  would 
shrink  away  from  the  exterior,  and  open  spaces  would 
come  into  existence  between  them.  But  the  nature  of 
matter  is  such  that  a  terrestrial  film  would  be  utterly  inca- 
pable of  sustaining  its  own  weight  if  any  adequate  force 
were  exerted  to  raise  it  into  an  arch  having  a  span  of  some 
miles.  The  solid  external  film  must  therefore  yield  in 
some  way  so  as  to  continue  to  rest  generally,  throughout 
its  whole  extent,  upon  the  underlying  nucleus.  Under  the 
enormous  lateral  pressure  which  would  ultimately  be  de- 
veloped, the  crust  may  be  conceived  as  either  crushing 
together,  or  undergoing  a  process  of  wrinkling  and  frac- 
ture, combined  in  certain  proportions.  Either  of  these 
consequences  may  be  conceived  as  somewhat  uniformly 
distributed  geographically,  or  as  localized  to  a  certain  ex- 
tent. The  theory  here  considered  supposes  the  result  to 
take  the  form  of  wrinkling,  and  supposes  it  to  be  unequally 
distributed.  If  this  conception  represents  the  actual  na- 
ture of  the  events,  then  wrinkles  or  folds  of  the  planetary 
crust  would  arise  which,  in  the  course  of  ages,  might 
naturally  be  conceived  to  grow  into  mountain  dimensions. 
The  process  of  wrinkling  through  the  action  of  lateral 
pressure  is  finely  illustrated  by  spreading  a  layer  of  clay  on 
a  stretched  sheet  of  India  rubber,  and  allowing  the  sheet 
slowly  to  contract.*  The  sheet  may  be  five-eighths  of  an 
inch  (16  mm.)  thick,  6£  inches  (12  cm.)  wide  and  16 
inches  (40  cm.)  long.  When  stretched  to  24  inches  (60 
cm.)  it  may  be  covered  with  a  layer  of  potter's  clay  from 
1  inch  to  2f  inches  (25  to  60  mm.)  thick,  made  as  adher- 

*  As  first  shown  by  M.  Alphonse  Favre  of  Geneva  (La  Nature,  1878),  from 
whom  the  accompanying  cut  — one  of  four  in  La  Nature,—  has  been  borrowed. 
See  also  Nature,  six,  103,  1878,  and  also  Rev.  O.  Fisher:  Physics  oftheEartKs 
Crust,  128.  In  this  connection  the  reader  should  also  refer  to  the  passage  pre- 
viously quoted  describing  the  cooling  of  a  molten  mass  in  the  operations  of  a 
puddling  furnace.  See  p.  219. 


298  A    COOLTXG    PLANET. 

rent  as  possible  to  the  India  rubber,  with  a  block  of  wood 
applied  at  each  end.  On  the  result  shown  in  the  annexed 
cut,  several  important  observations  may  be  made,  (a) 
The  strata  are  less  contorted  in  the  lower  layers  than  in 
the  upper.  (£>)  The  layers  are  disjoined  in  certain  places 
by  fissures  or  caverns,  (c)  They  are  traversed  by  clefts  or 
faults  inclined  or  vertical,  (d)  There  is  no  sort  of  sym- 
metry in  these  structures,  (e)  The  lateral  pressure  was 
exerted  only  from  two  opposite  directions,  and  not  as  in 
the  case  of  the  earth's  crust,  from  all  directions  ;  and 
hence  the  folds  reveal  longitudinality  or  an  axial  dimen- 
sion. (/)  The  corrugations  are  distributed  over  the 
whole  surface,  and  not  accumulated  in  "  chains  "  or  groups. 
The  importance  of  some  of  these  observations  will  appear 
hereafter. 

The  cooling  and  contraction  which  originate  orographic 
wrinkles  must  be  conceived  as  progressive  and  uniform. 
To  a  great  extent,  it  may  also  be  conceived,  the  evolution 
of  mountain  inequalities  would  be  progressive  and  uni- 
form. But  a  moment's  consideration  of  the  unequal  con- 
stitution and  rigidity  of  the  rocks,  and  especially  the  un- 
equal distribution  of  the  firmest  resistances  to  lateral 
pressure  —  especially  after  the  primordial,  fire-formed 
crust  should  have  been  once  disturbed  —  renders  it 
entirely  probable  that  the  progress  of  the  development  of 
surface  inequalities  would  be  somewhat  spasmodic  and 
convulsive.  This  theory,  therefore,  while  recognizing  an 
identity  of  forces  and  modes  of  action  in  ancient  and 
later  times,  provides  for  any  indications  which  may  be 
discovered,  of  cataclysmic  and  revolutionary  results  of 
accumulated  strains.  It  provides,  also,  for  more  energetic 
and  more  frequently  recurring  orographic  activities  in  the 
earlier  ages  of  the  world  than  in  the  later.  It  also  ex- 
plains why  later  mountain  up-lifts  should  exceed  the 
earlier  in  altitude,  since,  owing  to  the  increased  thickness 


OROGENIC    FORCES. 


299 


and  resistance  of  the  crust,  they 
could  only  have  been  produced 
after  a  longer  continued  and  more 
highly  intensified  accumulation  of 
strains.  It  is  apparent,  finally,  that 
this  theory,  taken  by  itself,  re- 
quires an  immense  number  of 
comparatively  short  wrinkles  run- 
ning in  every  conceivable  direc- 
tion over  the  earth's  surface,  like 
the  wrinkles  in  the  skin  of  a  shriv- 
elled apple.  The  theory  provides 
no  cause  for  a  tendency  toward 
determinate  directions  and  pro- 
longed continuity  in  the  wrinkles 
produced.  But  if  mountains  are 
developed  from  shrinkage  wrin- 
kles, we  must  explain,  also,  why 
they  are  disposed  in  ranges  and 
chains  of  ranges,  and  why  they 
tend  to  sustain  certain  uniform 
relations  to  the  meridian.  The 
general  theory  of  these  phenom- 
ena has  been  already  explained  in 
a  previous  part  of  this  chapter, 
and  its  particular  application  to 
the  earth  will  be  considered  in  the 
next  chapter,  when  treating  rather 
of  existing  phenomena  than  of 
antecedent  conditions. 

The  inauguration  of  a  wrinkle 
would  be  the  determination  of 
lines  of  weakness,  seen  in  cross 
section  at  a,  b,  c,  Figure  51,  par- 
allel with  each  other.  Evidently 


300 


A    COOLING    PLAXET. 


any  continued  tendency  to  wrinkle  would  be  most  readily 
developed  along  the  existing  wrinkle,  since  the  lateral  pres- 
sure B  G  would  be  resolved  at  G  into  the  two  components 
G  I  and  G  F,  the  latter  tending  to  develop  an  elevation  at 
G.  The  component  G  I  would  be  again  resolved  into  I  L 
and  I  a.  The  downward  stress  I  L  would  be  opposed  by 
the  underlying  matter,  which  would  contribute  a  part  of 
its  resistance  along  I  a,  and  another  part  along  I  G.  From 
the  opposite  direction,  A,  the  lateral  pressure  would  yield 
a  component  tending  to  depress  b,  and  that,  a  component 
tending  to  elevate  a.  The  two  components  meeting  at  a, 


FIG.  51.  FORMATION  OF  WRINKLES  IN  A  PLANETARY  CRUST  WITH   PARALLEL 
CONTIGUOUS  FURROWS.  CROSS  SECTION. 

would  give  a  vertical  or  subvertical  resultant  a  K.  Thus, 
a  wrinkle  once  inaugurated,  further  lateral  pressure  would 
tend  to  increase  its  elevation  and  deepen  the  parallel  depres- 
sions. The  weight  and  rigidity  of  the  primitive  fold  a,  finds 
always,  ultimately,  a  component  in  the  upward  force  G  F, 
as  explained,  and  this  increases  as  the  altitude  and  mass 
of  a  increase.  In  the  course  of  time,  therefore,  accessory 
folds  rise  at  G  and  H,  separated  from  the  main  fold  by  the 
furrows  b  and  c.  In  the  later  progress  of  these  events 
the  folds  at  G  and  H  repeat  the  action  of  the  fold  a.  Thus 
parallelism  of  mountain  ranges  would  result,  the  lateral 
ranges  of  course  diminishing  consecutively  with  increase 


OROGEXIC    FORCES.  301 

of  distance  from  the  central  fold,  and  at  the  same  time 
broadening  their  bases. 

The  history  of  wrinkling  must  be  regarded  as  begin- 
ning long  before  the  descent  of  the  ocean  ;  but  it  con- 
tinues through  all  the  cooling  asons  of  a  planet's  life. 
The  ocean's  waters  would  be  accumulated  to  greatest 
depths  in  the  deepest  depressions  between  the  wrinkles. 
When,  after  the  measure  of  the  oceans  should  be  filled, 
the  wrinkling  should  continue,  the  crests  of  the  primor- 
dial wrinkles  would  be  the  first  to  emerge.  Thus  the 
germs  of  the  continents,  and  afterward  the  continents 
themselves,  would  be  stretched  out  in  the  places  and  in 
the  attitudes  predetermined  before  the  ocean  accumulated. 
The  ocean  basins  and  the  ocean  shores  are  conformed  to 
the  preconfiguration  of  the  wrinkles.  The  location  and 
trends  of  the  mountain  chains,  therefore,  have  not  been 
determined  by  the  position  of  the  ocean's  mass,  for  the 
same  cause  has  determined  both.  The  ocean  has  pressed 
against  the  submerged  slopes  of  the  great  folds,  and  to 
some  extent  has  exerted  an  accessory  lateral  pressure. 
The  effect  of  this,  so  far  as  it  was  felt,  would  be  to 
increase  the  wrinkling  effects  and  possibly  (as  Dana  thinks) 
to  incline  the  folds  away  from  the  coast  line. 

The  error  must  be  avoided  of  conceiving  the  wrinkled 
condition  of  the  planetary  crust  as  restricted  to  the  land 
areas.*  Wrinkles  would  necessarily  exist  along  many 
meridians  on  all  sides  of  the  planet.  The  ocean  at  first 
would  cover  all ;  and  only  the  highest  folds  and  plateaux 
would  ever  emerge  above  the  ocean  level.  There  are 

*Rev.  O.  Fisher  assumes  (Physics  of  the  Earth's  Crust,  169, 179,  282,  283) 
that  surface  plications  have  not  been  developed  under  the  sea.  And  yet  he 
refers  in  another  place  (id.,  p.  78)  to  the  fact  that  "  contorted  strata  are  to  be 
also  found,  in  what  would  be  termed  level  countries,  often  covered  with  hori- 
zontal deposits  of  later  date'' — for  example,  the  highly  contorted,  carboniferous 
strata  of  parts  of  Belgium;  and  we  might  add,  the  contorted  Archaean  of  Can- 
ada and  New  York,  overlaid  by  horizontal  uncontorted  Potsdam  sandstone  and 
succeeding  formations. 


302  A    COOLING    PLANET. 

mountains,  valleys  and  plains  in  the  bottom  of  the  sea,  as 
well  as  over  the  continents.  The  widest  landscapes  are 
buried  beneath  cubic  miles  of  primitive  brine.* 

Professor  James  D.  Dana,  whose  thoughts  on  all  sub- 
jects are  suggestive  and  weighty,  has  devoted  to  the  the- 
ory of  mountains  more  study,  probably,  than  any  other 
American  geologist ;  and  the  whole  subject  of  a  shrinking 
globe  and  a  wrinkling  crust  has  been  considered  by  him 
from  every  point  of  view.f  Though  his  opinions  in  refer- 
ence to  a  fluid  nucleus  and  the  great  influence  of  the 
ocean,  and  probably  also,  on  the  subject  of  "mashing 
together"  (something  to  be  presently  explained)  have 
been  modified  by  the  progress  of  investigation,  he  has 
always  maintained  that  "the  principal  mountain  chains 
are  portions  of  the  earth's  crust  which  have  been  pushed 
up  and  often  crumpled  or  plicated  by  the  lateral  pressure 
resulting  from  the  earth's  contraction  ; "  that  the  oceanic 
areas  have  been  "the  regions  of  greatest  contraction  and 
subsidence,  and  that  their  sides  have  pushed  like  the  ends 
of  an  arch,  against  the  borders  of  the  continents,"  deter- 
mining the  border  position  of  orographic  and  volcanic 
phenomena ;  that  metamorphism  has  taken  place  only 

*See  the  section  from  Charleston,  S.  C.,  across  the  Gulf  Stream,  by  A.  D. 
Bache,  Proc.  Amer.  Assoc.,  1854,  141,  and  Diagram  9.  But  Bache's  conclusions 
are  not  confirmed  by  Commander  J.  K.  Bartlett,  Bulletin  No.  2,  Amer.  Geo- 
graph.  Soc.,  p.  73,  1882.  For  the  general  configuration  of  the  Atlantic  bottom, 
however,  see  C.  Wyville  Thompson :  Voyage  of  the  Challenger:  Depths  of  the 
Sta,  etc.  On  the  configuration  of  the  bottom  of  the  Pacific,  see  J.  D.  Dana, 
Rep.  Geol.  Wilkes  U.  S.  Expl.  Exped.,  4to,  1840,  p.  339,  and  Corals  and  Coral 
Islands,  8vo,  1872,  p.  329. 

tSee  a  summary  of  Professor  Dana's  views  in  Amer.  Jour.  Sci.,  Ill,  v,  483-5, 
with  references  to  numerous  earlier  publications  by  himself.  The  article  here 
referred  to  is  an  extended  memoir  embracing  his  final  conclusions  On  somt 
results  of  the  Earth's  Contraction  from  Cooling,  including  a  discussion  of  the 
Origin  of  Mountain*  and  ll/e  \atnre  if  the  Earth's  Interior,  Part  I,  Review  of 
opinions,  and  Tlieortj  of  )fon-  tain  Origin,  423-43,  June,  1873;  Part  II,  Condition 
of  the  Earth's  Intetioi,  and  connection  of  Facts  with  Mountain-making,  and 
Part  III,  Metamorphism,  id.  Ill,  vi,  6-14;  Part  IV,  Igneous  Ejections,  vi,  104-6; 
Part  V,  Formation  of  Continental  [Bateaux  and  Ocean  Depressions,  vi,  161-72, 
Sep.,  1873.  See,  also,  Dana's  Manual  of  Geology,  3d  edition. 


OROGENIC    FORCES.  303 

during  periods  of  disturbance,  and  he  now  thinks  that  the 
heat  required  has  been  derived  partly  from  the  earth's 
liquid  interior  and  partly  from  the  crushing  strains  (see 
beyond)  experienced  by  the  crust.  He  maintains  that 
wide  areas  have  experienced  geosynclinal  and  geanticlinal 
movements,  and  that  the  latter  are  not  accompanied  by 
plication  and  metarnorphism,  though  they  sometimes 
attain  low  mountain  altitudes,  and  supplement  the  eleva- 
tion of  characteristically  plicated  and  metamorphic 
mountain  chains. 

The  theory  of  wrinkling  over  a  molten  interior,  or  even 
a  fluid  zone,  has  been  objected  to  by  Professor  Joseph  Le 
Conte*  on  the  ground  that  the  materials  of  the  crust  do 
not  possess  sufficient  rigidity  to  sustain  themselves  much 
above  or  below  the  plane  of  fluid  equilibrium.  Hence  the 
great  folds  of  mountains  and  the  broader  arches  of  conti- 
nents and  plateaux,  as  well  as  the  depressions  of  the 
ocean  basins,  cannot  be  regarded  as  the  simple  phenomena 
of  wrinkling;  and  Professor  Le  Conte,  like  Archdeacon 
Pratt  f  and  Robert  Mallet,  J  refers  these  unequal  saliences 
of  the  crust  to  unequal  radial  shrinkage.  For  some  rea- 
son, as  he  thinks,  the  earth  has  contracted  more  along  the 
radii  under  the  depressions  than  along  those  under  the 
elevations;  and  the  earth  has  attained  sufficient  rigidity  to 
sustain  the  pressure  resulting  from  such  inequalities. § 
But  great  elevations  and  subsidences,  and  even  mountain 
folds,  are  known  to  have  been  produced  when  the  circum- 
stances are  such  as  to  prove  that  the  terrestrial  crust 

*  A  Theory  of  the  Formation  of  the  Great  Features  of  the  Earth's  Surface, 
Amer.  Jour.  Sci.,  Ill,  iv,  3-15,  Nov.,  1872. 

t  Pratt:  Figure  of  the  Earth,  4th  ed.,  200,  306,  1871. 

*  Mallet,  Trans.  Roy.  Soc.,  1873,  §§  52,  60.    Principal  J.  W.  Dawson  seems 
to  entertain  ii  similar  view,  as  indicated  in  his  Address  in  Science,  ii,  197,  Aug. 
17,  1883. 

§  Rev.  O.  Fisher,  however,  has  shown  that  the  whole  radial  contraction 
would  not  equal  the  difference  of  level  between  the  land  surface  and  the  sea 
bottom.—  Physics  of  the  Earth's  Crust,  79. 


304  A    COOLING    PLANET. 

possesses  sufficient  rigidity  to  sustain  the  saliences,  and 
sufficient  hypogeal  mobility  to  permit  them  sometimes  to 
return  to  older  positions.  Thus,  as  Professor  J.  D.  Dana 
has  reminded  us,*  the  region  about  Montreal  and  thence 
to  Lake  Champlain  and  the  coast  of  Maine  has  been  raised 
without  evidence  of  plications  from  200  to  500  feet  in 
late  Post-Tertiary  time;  and  some  of  the  higher  regions 
of  the  Rocky  Mountains  have  been  raised  8,000  to  10,000 
feet  since  the  Cretaceous  age,  and  there  is  no  reason  to 
suppose  that  any  disturbances  revealed  in  the  Cretaceous 
and  Tertiary  strata  have  been  the  cause  of  the  elevation. 
In  other  instances,  as  in  the  Alleghenies,  the  Uinta  and 
the  Sierra  Nevada,  as  shown  by  Lesley,  Powell  and  King, 
enormous  downthrows  have  taken  place,  to  the  extent  of 
10,000  to  25,000  feet;  and  these  are  most  naturally  explic- 
able on  the  theory  of  folds  and  arches  in  the  earth's  crust. 
In  fact,  it  is  a  common  thing  to  find  a  line  of  fault  passing 
into  a  fold  or  flexures,  as  for  instance,  in  the  region  of  the 
High  Plateaux  of  Colorado.  It  is  scarcely  conceivable 
that  the  flexure-continuation  of  a  fault  should  not  be  sus- 
tained by  its  own  strength  over  some  mobile  condition  of 
matter  ready  to  retreat  as  soon  as  the  strain  becomes  too 
great  for  the  material  to  withstand.  The  continuity  of 
folds  and  faults  is  well  illustrated  in  the  experiment  of 
Favre,  previously  described. 

That  folds  and  arches  actually  exist,  and  not  merely 
elevations  caused  by  crushing  together,  and  that  such 
folds  or  wrinkles  would  arise  upon  the  surface  of  an 
incrusting  globe  is  a  conclusion  so  well  sustained  by  facts 
and  opinions  that  we  may  venture  the  assertion  that  the 
difficulty  raised  by  Professor  Le  Conte  is  not  a  very  serious 
one. 

Captain  C.  E.  Dutton  has  urged  an  objection  which  is 
more  recondite.  He  questions  the  adequacy  of  contrac- 

*  Pana;  Resists  of  the  Earth's  Contraction,  Amer.  Jour.  Sci..  Ill,  v,  428, 


OROGEXIC    FORCES.  305 

tion  to  develop  the  rugosities  of  the  earth's  crust.  Start- 
ing from  Fourier's  solution  of  the  problem  of  the  "'rate  of 
variation  of  temperature  from  point  to  point,  and  the 
actual  temperature  at  any  point  in  a  solid  extending  to 
infinity  in  all  directions,  on  the  supposition  that  at  an 
initial  epoch  the  temperature  has  had  two  different  con- 
stant values  on  the  two  sides  of  a  certain  infinite  plane,'' 
and  using  Sir  William  Thomson's  application  of  the  solu- 
tion to  the  case  of  the  earth,  Captain  Button  finds  that 
on  any  supposition  as  to  present  rate  of  increase  of  tem- 
perature downward,  and  as  to  the  conductivity  of  the 
rocks,  "the  greatest  possible  contraction  due  to  secular 
cooling  is  insufficient  in  amount  to  account  for  the  phe- 
nomena attributed  to  it  by  the  contractional  hypothesis." 
"By  far  the  larger  portion  of  this  contraction,"  he  says, 
"must  have  taken  place  before  the  commencement  of  the 
Palaeozoic  age.  By  far  the  larger  portion  of  the  residue 
must  have  occurred  before  the  beginning  of  the  Tertiary; 
and  yet  the  whole  of  this  contraction  would  not  be  suffi- 
cient to  account  for  the  disturbances  which  have  occurred 
since  the  close  of  the  Cretaceous." 

Captain  Dutton  thinks,  also,  that  "the  determination 
of  plications  to  particular  localities  presents  difficulties  in 
the  way  of  the  contractional  hypothesis  which  have  been 
underrated."  The  localization  of  the  plications  is  only 
possible  on  the  assumption  of  a  large  amount  of  horizon- 
tal slipping  of  the  crust  over  the  nucleus,  and  this  would 
present,  even  over  a  liquid  nucleus,  an  amount  of  friction 
which  renders  the  assumption  a  physical  absurdity.* 
Wrinkling  resulting  from  uniform  cooling,  and,  conse- 
quently, uniform  shrinkage,  would  be  represented  by  the 
analogy  of  a  withered  apple,  instead  of  a  surface  present- 

*C.  E.  Dutton,  Amer.  Jour.  Sci.,  viii,  113-23,  Aug.,  1874.  See  also  Penn. 
Monthly,  May  and  June,  1870,  on  Theories  of  the  Earth's  Physical  Evolution, 
and  Oeol.  Mag.,  Decade  ii,  Vol.  iii,  327,  reviewed  in  Geol.  Mag.,  iv,  322. 


306  A    COOLING    PLANET. 

ing  in  one  region  one  continuous  system  of  plications 
extending  from  Cape  Horn  to  Behring's  Sea,  and  in  an- 
other, a  zone  a  thousand  miles  in  width,  from  the  Appa- 
lachians to  the  one  hundredth  meridian,  with  almost  no 
evidences  of  disturbance  presented. 

Rev.  O.  Fisher  has  also  made  objection  to  the  contrac- 
tional  theory.*  While  admitting  that  the  crumpling  of 
the  earth's  crust  reveals  the  action  of  lateral  pressure,  he 
shows  by  calculation  based  on  certain  assumptions  of  con- 
stant quantities,  that  the  elevations  above  a  datum  plane 
due  to  the  contraction  of  a  solid  earth,  would  not  form  a 
layer  exceeding  nine  hundred  feet  in  thickness,  while  the 
actual  elevations  above  the  same  plane  would  form  a  layer 
ten  thousand  feet  in  thickness.  The  compression,  there- 
fore, must  be  due  to  some  other  cause  than  contraction  of 
the  earth  through  loss  of  heat.  He,  therefore,  attempts 
to  establish  the  probability  that  the  crust  rests  on  a  fluid 
zone  in  a  state  of  igneo-aqueous  fusion,  and  that  the  escape 
of  steam  and  gases  into  fissures  formed  on  the  under  side 
of  the  crust  exerts  tho  lateral  pressure  which  has  contorted 
the  strata. 

Captain  Button's  assumption  that  the  contractional 
theory  implies  a  molten  nucleus  enables  him  to  argue  that 
at  the  beginning  of  incrustation  the  whole  earth  had  cooled 
nearly  to  the  point  of  solidification.  But,  it  may  be  held, 
as  it  is  generally  held,  that  the  terrestrial  nucleus  began  to 

*  O.  Fisher :  Physics  of  the  Ea,  We  Crust,  ch.  iv,  London,  1881.  Mr.  Fisher's 
views  on  vulcanism  and  orogeny  have  mostly  appeared  in  previous  periodical 
publications.  See,  especially,  On  the  Elevation  of  Mountain  Chains  by  Lateral 
Pressure,  Trans.  Cambr.  Phil.  Soc.,  xi.  Part  II,  18 ;  Part  III,  489, 1868 ;  On  Elevation 
and  Subsidence,  Phil.  Mag.,  1872 ;  On  the  Formation  of  Mountains  and  the  Hypoth- 
esis of  a  Liquid  Substratum  beneath  the  Earth's  Crust,  Proc.  Cambr.  Phil.  Soe., 
Feb.  22,  1875;  Mountain-making;  The  Inequalities  of  the  Earth's  Surface  Viewed 
in  Connection  with  Secular  Cooling,  Trans.  Cambr.  Phil.  Soc.,  xii.  Part  I,  505: 
Part  II,  431,  abstract  in  Amer.  Jour.  Sci.,  Ill,  x,  389-90;  Remarks  upon  Mr.  Mal- 
let's T/ieory  of  Volcanic  Energy,  Quar.  Jour.  Geol.  Soc..  London,  xxxi,  469-78, 
May  12, 1875;  Mr.  Mallet's  Theory  of  Volcanic  Energy  Tested,  Phil.  Mag..  IV,  i, 
302-19,  Oct.,  1875;  id.  V.i,  138-42. 


OROGENIC   FORCES.  307 

solidify  at  a  temperature  much  above  the  point  of  liquefac- 
tion under  atmospheric  pressure.  If  so,  the  process  of 
equalization  of  temperature  by  convection  could  be  carried 
on  only  in  the  region  exterior  to  the  consolidated  nucleus, 
and  when  incrustation  began,  a  very  high  temperature  was 
shut  up  in  the  nucleus.  A  greater  amount  of  cooling  and 
contraction  must  therefore  take  place  than  would  be  pos- 
sible on  Captain  Button's  assumption  of  a  liquid  nucleus 
at  a  lower  temperature.  Moreover,  Captain  Dutton  as- 
sumes, with  Sir  William  Thomson,  that  as  fast  as  surface 
materials  solidified,  they  would  sink  by  their  increased 
density  into  the  fluid  mass,  until  the  late-formed  and  com- 
paratively cooled  solid  nucleus  should  have  grown  nearly 
to  the  surface.  This  would  be  an  additional  cause  of  gen- 
eral reduction  of  internal  temperature.  But  the  theory  of 
a  sinking  crust  can  scarcely  stand,  in  the  light  of  recent 
researches,  already  cited,  on  the  relative  densities  of  freshly 
solidified  masses,  and  the  molten  magmas  from  which  they 
were  derived.  It  is  much  more  probable  that  incrustation 
began  at  an  early  stage,  and  at  once  began  to  arrest  escape 
of  internal  heat,  so  that  since  the  first  incrustation,  the  in- 
terior has  undergone  a  larger  amount  of  shrinkage  than 
Captain  Dutton  admits.*  Still,  it  must  be  borne  in  mind 
that  an  initial  temperature  of  7000°  Fahr.  is  assumed,  and 
this  is  probably  3000°  above  the  melting  temperature  of 
silicious  rocks  under  atmospheric  pressure.  Undoubtedly, 
the  results  exhibited  by  Captain  Dutton  and  Rev.  Mr. 
Fisher  respecting  the  inadequacy  of  all  probable  contrac- 
tion through  cooling,  to  develop  the  necessary  tangential 
pressure,  must  be  very  carefully  considered.  But  while 
the  effects  of  contraction  remain  too  clearly  indicated  to 
be  mistaken,  and  while  all  admit,  as  they  must,  that  some 
contraction  must  have  resulted  from  cooling,  it  seems  ra- 

*  Compare  remarks  by  A.  H.  Green,  Nature,  xxv,  481,  relative  to  the  initial 
temperature  of  7000°. 


308  A    COOLING    PLANET. 

tional  to  maintain  that  the  theoretical  estimates  of  the 
results  of  possible  contraction  are  vitiated  by  some  unde- 
tected errors  in  the  principles  assumed  or  the  constants 
employed. 

As  to  Captain  Dutton's  objection  that  the  formation  of 
a  mountain  range  is  impossible  upon  a  globe  contracting 
equally  along  all  its  radii,  this  seems  well  taken,  and  I 
know  of  no  way  to  meet  it  on  principles  generally  recog- 
nized by  geologists.  As  to  myself,  however,  I  am  at  once 
reminded  of  the  tidal  influences  already  discussed.  Here- 
after, in  treating  of  the  physiographic  features  of  our 
planet,  I  shall  point  out  the  remarkable  correspondences 
between  the  orographic  trends  and  the  structural  lines 
which  I  believe  must  have  been  wrought  by  tidal  action  in 
the  primitive  crust.  I  strongly  believe  that  in  this  is  to  be 
found  the  only  explanation  of  the  difficulty  suggested. 

As  to  the  improbability  of  the  requisite  slipping  of  the 
crust  to  develop  mountain  ranges  along  certain  meridians, 
with  broad  continental  plains  intervening,  I  am  inclined  to 
disagree  with  Captain  Button.  With  an  underlying  liquid 
or  plastic  layer  nearly  or  quite  continuous,  and  meridional 
predispositions  and  lines  of  weakness  preexisting,  it  seems 
to  me  probable  that  regions  of  sound  crust  unaffected  by 
any  predisposition  to  folding,  would  possess  sufficient 
rigidity  to  undergo  the  requisite  local  translation,  and  to 
press  with  the  requisite  force  against  rising  folds,  and.  even 
to  press  their  bases  under  and  cause  their  summits  to  over- 
hang toward  the  continental  side  —  a  result  exhibited  re- 
markably in  the  Alps,  where  the  pressure  from  both  sides 
has  been  such  as  to  develop  overhanging  in  both  directions 
from  the  centre,  producing  the  well  known  fan-shaped 
structure.  This  is  admirably  seen  in  a  section  across 
Mont  Blanc,  where  the  Jurassic  strata  and  underlying 
crystalline  schists  of  Val  Veni  have  been  overturned 
toward  the  south,  and  the  same  formations  in  the  valley  of 


OKOGENIC    FORCES.  309 

Chamounix  have  been  overturned  toward  the  north,  while 
the  central  protogine  mass  rests  like  a  protruded  bulge  be- 
tween the  two  sets  of  schists.  Hard  by  in  the  Brevent, 
the  crystalline  schists  have  again  been  squeezed  to  a  verti- 
cal attitude,  but  the  protogine  was  not  forced  up  in  the 
middle.  The  contracted  base  of  a  great  terrestrial  fold  is 
also  seen  in  the  St.  Gotthard  mass,  included  in  the  accompa- 
nying section  through  the  Alps.  The  restored  folds  of  this 
section,  indicated  by  the  dotted  lines,  convey  irresistibly  the 
impression  of  action  from  the  sides.  (See  next  page.) 

The  probability  of  crustal  slipping  is  expressly  recog- 
nized by  Dr.  Dawson,  who,  speaking  of  past  movements 
of  the  earth's  crust,  says  :  *  "  One  patent  cause  is  the 
unequal  settling  of  the  crust  toward  the  centre;  but  it  is 
not  so  generally  understood  as  it  should  be,  that  the 
greater  settlement  of  the  ocean  bed  has  necessitated  its 
pressure  against  the  sides  of  the  continents  in  the  same 
manner  that  a  huge  ice-floe  crushes  a  ship  or  a  pier.  The 
geological  map  of  North  America  shows  this  at  a  glance, 
and  impresses  us  with  the  fact  that  large  portions  of  the 
earth's  crust  have  not  only  been  folded,  but  pushed  bodily 
back  for  great  distances.'11 

The  pressure  from  the  continental  side  of  a  fold  should 
establish  a  relation  between  the  height  of  a  mountain-fold 
and  the  breadth  of  the  continental  area  which  has  not  been 
affected  by  the  plications  due  to  it,  but  which  have  been 
accumulated  along  its  borders.  In  any  event,  the  folds 
exist,  and  however  caused,  the  same  necessity  of  slipping 
over  uncorrugated  areas  would  arise. f 

But  finally,  when  we  contemplate  the  physical  situation 

*  J.  W.  Dawson,  address  at  Minneapolis,  as  retiring  president  of  the  Ameri- 
can Association.  Science,  August  17,  18&3.  Quoted  only  for  the  passage  itali- 
cised, since  the  cause  assigned  would  not  tend  to  produce  the  effect  alleged,  but 
rather  a  wrinkling  of  the  ocean  bottom.  \ 

t  The  evidences  of  pressure  from  the  continental  side  are  recognized  in  the 
White  Mountain  region  by  C.  H.  Hitchcock  (Geol.  of  Neiv  Hampshire,  i,  519). 


310 


A   COOLING    PLANET. 


OROGENIC    FORCES.  311 

in  that  "  analytic  spirit "  which  Captain  Button  recom- 
mends, it  is  apparent  that  the  question  of  slipping  does 
not  properly  arise.  By  hypothesis,  the  crust  is  underlaid 
by  a  liquid  zone  or  a  liquid  nucleus.  The  shrinkage  of 
the  nucleus  develops  the  lateral  pressure  in  the  crust;  and 
the  surface  of  the  shrinking  nucleus  has  all  the  motion 
here  attributed  to  the  crust,  though  less  localized.  The  de- 
termination of  the  parts  of  the  crust  to  yield  to  the  pres- 
sure depends  only  on  the  location  of  the  weakest  regions. 
Points  in  the  crust  adjust  themselves  in  position  accord- 
ingly. If  any  friction  arises  between  the  crust  and  the  un- 
derlying- fluid,  the  fluid  being  free  to  move,  moves  with  the 
crust,  and  the  resistances  offered  to  the  adjustments  result- 
ing from  relief  from  pressures  of  inconceivable  magnitude 
are  too  inconsiderable  to  be  mentioned  in  this  connection.* 
The  expedient  by  which  Mr.  Fisher  attempts  to  pro- 
vide the  requisite  amount  of  tangential  pressure  in  default 
of  adequate  contraction,  is  certainly  original,  if  not  a 
h^avy  strain  upon  credulity.  Should  the  assumed  state 
of  igneo-aqueous  fusion  be  granted,  and  should  the  exist- 
ence of  innumerable  fissures  be  also  granted,  in  a  crust 
already  so  squeezed  by  contraction  as  to  close  every  open- 
ing, it  is  still  extremely  difficult  to  admit  that  the  penetra- 
tion of  the  fissures  by  elastic  vapors  furnishes  an  adequate 
cause  for  mountain  corrugations.  As  before  stated,  the 
utmost  energy  of  confined  vapors  is  insufficient  to  raise 
the  mountains  and  crush  the  crust.  Movements  of  eleva- 
tion, moreover,  have  been  slow,  persisting  through  geo- 
logic aeons;  these  are  not  the  characteristics  of  the  action 
of  elastic  vapors.f 

*  If  Captain  Button  will  turn  to  Baltzer's  Der  Glarnlsch  em  Problem  Alpinen 
Gebirgtsbaues,  he  will  find  a  section  which,  under  the  interpretation  given,  de- 
monstrates extensive  slipping,  not  only  over  a  liquid  magma,  but  over  older  and 
consolidated  formations;  and  not  only  slipping,  but  an  amazing  system  of  folds 
affecting,  for  instance,  the  Cretaceous  and  Eocene  strata,  without  corresponding 
folds  in  the  Jurassic  and  Triassic  strata. 

t  Compare  the  criticisms  of  A.  H.  Green,  Nature,  xxv,  481,  March  23,  1882. 


312  A    COOLING    PLANET. 

The  theory  of  lateral  pressure  through  nuclear  contrac- 
tion is  accepted  in  its  general  features  by  Professor 
Albert  Heim  of  Zurich,*  one  of  the  most  thorough  and 
competent  investigators  of  recent  times.  Heim,  however, 
to  the  contractional  theory  adds  a  subsidiary  hypothesis. 
He  holds  that  the  great  pressure  exerted  on  the  deeper 
strata,  say  below  3,000  meters,  reduces  them  to  a  plastic 
state.  Thus,  while  the  overlying  more  recent  sediments 
attain  and  retain  real  rocky  rigidity,  the  crystalline  schists 
acquire  a  condition  in  which  lateral  pressure  more  readily 
develops  folds  and  plications.  Thus  it  often  happens  that 
movements  of  the  crumpling  deeper  strata  carry  the  rigid 
overlying  strata  by  a  slipping  movement  over  considerable 
distances,  until  the  accumulated  strain  results  in  a  local 
fold  of  the  newer  and  more  rigid  strata,  as  in  the  remarka- 
ble case  of  the  GlSrnisch  section  described  by  Baltzer. 
Dr.  Friedrich  Pfaff  of  Erlangen,f  however,  argues  against 
the  hypothesis  of  deep  plasticity,  maintaining  that  the 
deepest  portions  of  the  earth  would,  on  this  theory,  be  the 
most  fluid,  and  the  earth  would  thus  be  destitute  of  the 
rigidity  demanded  by  astronomical  conditions.  He  main- 
tains further,  that  mountain  phenomena  are  such  as  de- 
mand rigidity  for  the  explanation  of  upheaval  and  fold- 
ing, since  plastic  masses  are  shown  by  experiment  to  yield 
quite  different  phenomena,  both  when  pressed  and  when 
exerting  pressure. 

Dr.  Pfaff,  after  a  careful  examination  of  the  contrac- 
tional theory,  concludes  that  it  is  inadequate  to  explain 
certain  phenomena  of  mountain  formation.  His  objec- 
tions may  be  stated  as  follows:  (1)  Cooling  would  not  neces- 
sarily produce  the  requisite  contraction.  If  it  should 
do  so,  there  is  implied  (a)  A  temperature  in  the  fluid  in- 

*Heim:  Untersuchungen  fiber  den  Mechanismus  der  Gebirgsbildung,  2  vols. 
A  work  embodying  the  .results  of  long  and  tireless  research. 

t  Pfaff:  Der  Mechanismus  der  Gebirgsbildung,  8vo.,  143  pp.,  1880. 


OROGEXIC   FORCES.  313 

terior  much  higher  than  the  melting  point  of  rock,  and  at 
the  same  time,  (b)  A  cooling  of  the  interior  much  more 
rapid  than  that  of  the  surface.  These  two  implications 
conflict,  as  he  thinks,  with  each  other.  (2)  The  whole 
thickness  of  the  crust  must  have  suffered  folding  simulta- 
neously, and  this,  in  some  cases,  is  not  the  fact,  since  the 
upper  or  lower  formations  have  been  separately  folded. 
(3)  The  folds  are  localized  instead  of  being  generally  dis- 
tributed over  the  surface.  (4)  The  folds  extend  in  long- 
ranges  of  determinate  direction,  instead  of  being  promis- 
cuously disposed.  (5)  The  newer  formations  have  received 
more  extensive  folds  than  the  older,  whereas  progressive 
cooling  should  result  in  progressively  diminishing  contrac- 
tional  results.  The  second,  third  and  fourth  objections 
are  considered  the  most  serious. 

As  to  Dr.  Pfaff's  first  objection,  I  think  it  loses  its  force 
in  view  of  general  considerations  heretofore  presented. 
As  to  the  second,  we  may  admit  that  the  whole  crust 
would  be  subjected  to  similar  action,  but  we  might  rea- 
sonably expect  the  visible  results  to  be  differently  devel- 
oped in  formations  of  different  constitution  and  rigidity, 
and  acted  on  by  different  superincumbent  pressures. 
Deep-seated  plasticity,  for  instance,  as  Heim  suggests, 
may  be  reasonably  conceived  a  true  explanation  of  discord- 
ant movements  in  the  upper  and  the  deeper  portions  of  the 
crust;  though  the  plasticity  supposed  need  not  be  attrib- 
uted solely  to  pressure,  but  partly  to  the  effect  of  heat 
and  water  in  a  zone  more  shallow  than  that  where  com- 
pression results  in  solidification.  As  to  the  third  and 
fourth  objections,  they  will  be  recognized  as  identical  with 
certain  ones  urged  by  Captain  Dutton,  and  their  removal 
results,  as  I  have  shown,  from  the  recognition  of  the 
effects  of  tidal  action  on  an  incrusting  planet.  As  to  the 
fifth  objection,  it  seems  to  assume  that  the  newer  forma- 
tions have  been  more  disturbed  because  they  have  been 


314  A   COOLING   PLANET. 

wrought  into  larger  folds.  There  is  no  other  evidence. 
But  the  premises  of  the  objection  probably  invert  the 
facts.  The  older  strata  have  been  most  disturbed.  But 
in  the  earlier  and  thinner  condition  of  the  crust,  lateral 
pressure  developed  more  numerous  plications  and  a  greater 
amount  of  crushing;  in  the  later  condition,  increased 
rigidity  resisted  pressure  until  the  strain  accumulated  to 
such  an  extent  as  to  evolve  movements  more  extensive 
vertically,  though  much  less  numerous. 

Dr.  Pfaff,  however,  chooses,  for  the  present,  to  set  aside 
the  contractional  theory,  and  in  its  place  offers  the 
hypothesis  that  large  quantities  of  water  finding  their  way 
into  the  crust,  by  some  means  which  he  does  not  explain  * 
excavate  vast  cavities,  and  that  the  subsidence  of  the  over- 
lying strata  gives  rise  to  the  dislocations  which  thus  affect 
the  upper  and  not  the  deeper  portions  of  the  crust,  It 
does  not  seem  to  occur  to  Dr.  Pfaff  that  this  hypothesis 
involves  greater  difficulties  than  the  theory  for  which  it  is 
proposed  as  a  substitute. 

The  theory  of  mountain  origin  through  wrinkling  of 
the  crust  may  suffice  to  explain  elevation,  volcanic  and 
seismic  actions,  and  even  metamorphism  and  plications; 
but  there  are  two  characteristics  of  mountain  corrugations 
which  this  theory  cannot  explain.  These  are  the  great 
thickening  of  the  formations  involved  in  the  corrugations, 
and  the  greatly  increased  fragmented  condition  of  the 
sediments.  To  supply  these  deficiences  in  orogenic  theory 
other  speculations  have  been  promulgated,  which  I  will 
now  concisely  explain. 

3.  Theory  of  Copious  Sedimentation  along  Geosyn- 
clinalf*. — In  1857,  Professor  James  Hall,  in  a  presidential 
address  before  the  American  Association  at  Montreal, 
enunciated  the  doctrine  that  the  enormous  thickening  of 

*"Wir8ind  bis  jctzt  allerdings  nicht  im  Stande,  darlibcr  genaue  Anskunft 
zu  geben,  wir  Wissen  nur,  das  wasn-er  in  die  grossten  Tiefen  hinabdringt,  aber 
nichts  Sicheres  flber  seine  Wirkung  daselb?t.v-  Op.  cit.,  119. 


OROGEXIC    FORCES.  315 

the  formations  along  the  Appalachian  chain  was  due  to 
the  prolonged  accumulation  of  sediments  along  a  sinking, 
off-shore  line  of  sea-bottom.  The  study  of  the  Appala- 
chians and  other  American  mountain  regions  led  him  to 
the  enunciation  of  a  general  theory,  of  which  the  princi- 
pal points  are  the  following:  Coast  regions  are  the  courses 
of  marine  currents,  and  hence  of  deposited  sediments. 
The  accumulation  of  sediments  by  their  gravity  gradually 
sinks  the  crust,  and  thus  a  great  thickness  is  attained; 
the  rocks  become  solidified  and  crystallized  below.  The 
continents  are  afterward  somehow  raised  —  not  the  moun- 
tain regions  separately.  The  mountains  are  shaped 
out  of  other  sediments  by  denudation  —  as  James  Hutton 
had  previously  argued.  Metamorphism  is  due  to  "mo- 
tion," "fermentation"  and  a  little  heat  —  the  last  coming 
up  from  below  in  consequence  of  the  increasing  accumu- 
lations at  the  surface.*  A  summary  of  these  views,  and 
to  some  extent,  a  commentary  on  them,  was  published  by 
Dr.  T.  S.  Hunt,  in  1858.f  Dr.  Hunt  entertains  generally 
the  same  views  as  Professor  Hall,  and  indeed  preceded 
him  in  the  conception  of  a  softened  plastic  zone  in  a  state 
of  igneo-aqueous  fusion,  situated  between  the  consolidated 
crust  and  the  solid  nucleus;  though  he  was  also  preceded 
in  this  by  KefersteinJ  and  Sir  John  Herschel.§  Dr.  Hunt 
places  greater  stress  than  Professor  Hall  on  the  influence 

*  Prof.  Hall's  address  is  published  only  in  the  Introduction  to  vol.  iii.  Pa- 
laeontology of  New  York.  [By  a  resolution  of  the  Standing  Committee  of  the 
Association,  in  August,  1882,  the  address  is  to  be  published  by  the  Association, 
after  an  interval  of  twenty-five  years.]  See  criticisms  by  J.  D.  Dana,  Amer. 
Jour.  Sci.,  II,  xlii,  205-11. 

tT.  S.  Hunt,  Canadian  Journal,  March  7,  1858;  Quar.  Jour.  Geol.  Sci., 
Nov.,  1859;  Amer.  Jour.  Sci.,  II,  xxxi,  411.  See,  also,  correlated  views  in  Amer. 
Jour.  Sci.,  II,  1,  21,  and  Geol.  Mag.,  June,  1869,  on  The  Probable  Seat  of  Volcanic 
Action  ;  also,  Amer.  Jour.  Sci.,  Ill,  v,  264-70.  Prof.  Hall's  theory  is  in  part 
accepted  by  Geo.  L.  Vose  in  Orographic  Geology,  1866,  47-55.  134. 

*Keferstein:  Katurgeschichte  des  Erdkorpers,  1834,  vol.  i,  109;  Bull.  Soc. 
gMog.  de  France,  I,  viii.  19',. 

§  Sir  John  Herschel,  Proc.  Geol.  Soc.,  London,  1836,  ii,  548;  Babbage's  Ninth 
Bridgeu-ater  Treatise,  Note  I,  225-57. 


316  A    COOLING    PLAXET. 

of  softening.  He  conceives  the  most  important  result  of 
the  subsidence  to  be,  to  "cause  the  bottom  strata  to  estab- 
lish lines  of  weakness  or  of  least  resistance  in  the  earth's 
crust,  and  thus  determine  the  contraction  which  results 
from  the  cooling  of  the  globe  to  exhibit  itself  in  those 
regions,  and  along  those  lines  where  the  ocean's  bed  is 
subsiding  beneath  the  accumulated  sediments."  While 
Professor  Hall  had  conceived  the  process  of  subsidence  as 
the  principal  cause  of  the  corrugations  of  the  strata,  Dr. 
Hunt  regarded  the  subsidence  rather  as  the  occasion  which 
determined  the  position  and  direction  of  the  corrugations, 
while  the  cause  of  the  displacements  and  metamorphism 
was  the  contraction  of  the  earth's  nucleus,  and  of  the 
deep-seated  sediments  themselves. 

Professor  Joseph  Le  Conte  has  entertained  a  similar 
view*  as  to  the  cause  of  subsidence.  "Suppose,"  he 
says,  "  sediments  accumulating  along  the  shores  of  a  con- 
tinent, the  first  effect  is  lithification,  and  therefore,  increas- 
ing density,  and  therefore,  contraction  and  subsidence, 
paripassu  with  the  deposit.  Next,  if  the  sedimentation 
continues,  follows  aqueo-igneous  softening,  or  even  melt- 
ing, not  only  of  the  lower  portion  of  the  sediments  them- 
selves, but  of  the  underlying  strata  upon  which  they  were 
deposited.  The  subsidence  probably  continues  during 
this  process.  Finally,  this  softening  determines  a  line  of 
yielding  to  horizontal  pressure,  and  a  consequent  upswell- 
ing  of  the  line  into  a  chain.  Thus  are  accounted  for, 
first,  the  subsidence,  then  the  subsequent  upheaval,  and 
also  the  metamorphism  of  the  lower  strata  so  universal  in 
great  mountain  chains"  (p.  468). f  Professor.!.  D.  Dana 
attributes  the  subsidence  chiefly,  at  least,  to  lateral  pres- 

*  J.  Le  Conte,  A  Theory  of  the  Formation  of  the  Great  Features  of  the 
Earth's  Surface,  Amer.  Jour.  Sci.,  Ill,  iv,  345-55,  460-72,  Nov.  and  Dec.,  1872. 

t  Subsidence  under  weight  of  sediments  is  recognized  by  J.  S.  Gardner  and 
Dr.  Charles  Ricketts  in  communications  to  the  Geological  Section  of  the  British 
Association  in  1882.—  Nature,  xxvi,  468,  469,  Sept.  7,  1S82.  See,  also,  note  p.  334. 


OROGEXIC    FORCES.  317 

sure.  He  holds  distinctly,  also,  to  a  real  local  elevation  of 
the  crust  along  a  mountain  geosynclinal,  at  the  end  of  the 
subsidence,  attended  by  plication  and  metamorphism.  He 
holds  also,  that  real  elevations  occur  sometimes  without 
plication  and  metamorphism.* 

This  theory  offers  a  probable  explanation  of  the  aug- 
mented thickness  of  mountain  formations,  f  but  physical 
geologists  will  scarcely  indorse  the  presumption  that  the 
formation  of  a  geosynclinal  is  due  to  an  accumulation  of 
sediments.  It  is  indeed,  frequently  asserted  that  delta 
regions  are  generally  in  process  of  subsidence  under  the 
weight  of  deposits;  but  it  is  scarcely  credible  that  a  crust 
possessing  sufficient  rigidity  to  sustain  the  weight  of  moun- 
tains, would  be  subject  to  depression  under  the  load  of  a 
few  feet  of  sediments  buoyed  up  by  immersion  in  the  seaj. 
Moreover,  Mr.  Clarence  King  has  shown§  that  subsidence 
has  in  some  cases  accompanied  unloading  of  sediments, 
and  the  accumulation  of  sediments  has  been  attended  by 
"upheaval.  The  theory  apparently  inverts  the  relative 
positions  of  cause  and  effect.  ||  If,  however,  subsidence 
from  nuclear  contraction  or  any  other  cause  is  taking  place 
along  a  shore,  this  depression  will  naturally  determine  the 
place  of  excessive  accumulation  of  sediments,  especially 
if  an  ocean  current  corresponds  in  position  and  direction. 

*  Dana,  Results  of  the  Earth's  Contraction,  Amer.  Jour.  Sci.,  Ill,  v,  423  43, 
June,  1873,  continued,  ib.,  vi,  6-14,  104-6,  161-72. 

t  Prof.  J.  D.  Whitney  ascribes  the  thickening  of  the  formations  reposing 
along  the  flanks  of  a  granite  axis  to  the  denudation  of  this  axis  after  upheaval  in 
the  midst  of  the  ocean.  (J.  D.  Whitney:  Mountain  Building.  Also,  North 
American  Review,  cxiii,  235-74.)  How  high  must  the  axis  have  been  to  supply 
the  requisite  amount  of  sediments  in  any  average  case? 

J  Compare  Fisher.  Geographical  Magazine,  x,  248. 

|  King :    Geology  of  the  Wth  Parallel,  i,  357,  732. 

II  Nevertheless  M.  Faye  attributes  even  greater  effects  to  accumulation  of 
burdens  upon  the  ocean's  bottom.  This  depression  of  the  sea-bottom  is  recip- 
rocated, he  thinks,  by  the  elevation  of  continents  and  mountain  chains.  To  the 
weight  of  sediments,  however  is  added,  on  his  theory,  the  effect  of  increased 
thickening  of  the  cooled  crust  under  the  ocean.— Faye,  Annuaire  du  Bureau 
des  Longitudes,  1881. 


318  A    COOLING    PLANET. 

This  theory  also  explains  the  coarsely  fragmental 
character  of  the  deposits,  especially  if  the  depression  is 
overflowed  by  an  ocean  current  bringing  sediments  from  a 
crumbling  coast,  as  was  suggested  by  Professor  Hall,  who 
posited  a  wasting  continent  to  the  northeast  of  the  Ap- 
palachian geosynclinal. 

The  theory  is  unsatisfactory,  however,  on  two  additional 
points.  Perhaps  it  should  be  said  the  theory  is  incom- 
plete. It  does  not  offer  an  adequate  explanation  of  moun- 
tain saliences.  That  some  mountains  are  strictly  results 
of  neighboring  erosions  cannot  be  doubted.  Nor  is  it 
easier  to  doubt  that  others  have  originated  through 
some  sort  of  local  elevation.  Very  few  American  or 
European  mountains  indicate  by  their  structure  that  they 
are  mere  remnants  of  wasted  continents.  The  dips  of  the 
strata  flanking  them  almost  universally  demonstrate  that 
uplifts  have  taken  place  which  have  inclined  the  sheets  of 
sediments  along  each  side.  Nor  does  the  theory  offer  an 
adequate  explanation  of  the  enormous  amount  of  plication 
and  crumpling  which  generally  accompany  mountain  forms. 
It  seems  to  conceive  the  synclinal  trough  filled  by  sedi- 
ments to  a  state  of  convexity  and  so  maintained  while 
slowly  sinking.  The  sinking  process  effects  the  plication. 
Now  the  plication,  in  many  cases,  amounts  to  at  least  twice 
the  horizontal  extent  of  the  formation,  and  this  would  re- 
quire in  a  synclinal  twenty-five  miles  wide,  a  vertical  alti- 
tude of  fifty  miles.  In  any  ordinary  case  of  crumpling  or 
plication,  the  altitude  must  have  been  equal  to  the  breadth 
of  the  synclinal,  or  so  nearly  equal  to  it  as  to  annihilate 
all  presumption  in  favor  of  the  theory.  Dr.  Hunt  joins  to 
this  action  the  secular  contraction  of  the  earth's  nucleus, 
and  Professor  J.  Le  Conte,  Professor  J.  D.  Dana  and  others 
assign  secular  contraction  alone  as  the  cause  of  plications 
along  a  filling  geosynclinal.  The  latter  two  also  main- 


OROGENIC    FORCES.  319 

tain  that  the  plications  were  produced  chiefly  at  the  end 
of  the  process  of  subsidence. 

4.  Theory  of  Masking  Together. — In  1872,  Mr.  Robert 
Mallet,  an  eminent  English  engineer,  propounded*  the 
theory  that  the  secular  contraction  of  the  earth's  nucleus 
had  developed  tensions  in  the  crust,  which  found  relief  in 
the  local  crushing  of  the  rocks  along  lines  of  relative  weak- 
ness, and  thus  heat  was  evolved  by  transformation  of  me- 
chanical energy.  Mr.  Mallet,  however,  maintained  that  in 
the  earlier  condition  of  the  earth,  while  the  crust  was  thin- 
ner, tangential  thrust  had  developed  mountain  folds,  where- 
as, in  modern  times,  it  develops  chiefly  vulcanic  and  seismic 
phenomena.  He  substantiated  his  theory  by  a  citation  of 
many  results  of  the  experimental  crushing  of  rock  frag- 
ments, and  calculated  that  the  total  heat  escaping  through 
volcanic  vents  is  fully  accounted  for  by  the  thermal  effects 
of  the  secular  crushing  of  the  crust,  while  the  normal 
radiation  is  supplied  by  slow  conduction  from  the  primi- 
tively heated  interior.  Mr.  Mallet  subsequently  enforced 
these  views  by  many  observations,  experiments  and  calcu- 
lations.f 

*  Mallet,  Volcanic  Energy,  an  Attempt  to  Develop  its  True  Origin  and  Cos- 
mical  Relations,  Proc.  Roy.  Soc.,  No.  136,  1872,  Phil.  Trans.,  1873,  pt.  i,  147,  ab- 
stract in  Amer.  Jour.  Sci.,  Ill,  iv,  409-13;  vii,  145-8;  additions  to  this,  Phil. 
Trans.,  1875,  clxv,  pt.  i,  abstract  in  Amer.  Jour.  Sci.,  Ill,  viii,  140-1.  For  criti- 
cisms and  comments  on  Mallet's  theory  see  Sir  William  Thomson,  Nature,  Jan. 
18  and  Feb.  1, 1872  (compared  with  which  see  J.  G.  Barnard,  Smithsonian  Contri- 
butions, No.  240,  and  Sir  W.  Thomson's  later  publications,  with  modified  views); 
D.  Forbes,  Nature,  Feb.  6,  1872 ;  F.  W.  Huttou,  Nature,  Nov.  27, 1873 ;  E.  W. 
Hilgard,  Amer.  Jour.  Sci.,  Ill,  vii,  535-46,  June,  1874,  and  Phil.  Mag.,  July,  1874, 41. 

t  Robert  Mallet,  On  the  Temperature  Attainable  by  Rock-crushing,  and  its 
Consequences,  Phil.  Mag.,  July,  1875,  1-13,  and  Amer.  Jour.  Sci..  Ill,  x,  256-68, 
xii,  463;  Phil.  Mag.,  V,  i,  19-22.  See,  also,  Mr.  Mallet's  Introduction  to  L. 
Palmieri's  work  on  the  Eruption  of  Vesuvius  in  1872,  entitled,  On  the  Present 
State  of  Knou'ledge  of  Terrestrial  Vulcanicity,  the  Oosmical  Mature  and  Rela- 
tions of  Volcanoes  and  Earthquakes,  abstract  in  Amer.  Jour.  Sci.,  Ill,  v,  219-25. 
Numerous  other  publications  by  Mr.  Mallet  bearing  more  particularly  on  the 
science  of  volcanoes  and  earthquakes  may  be  found  in  Tranx.  Roy.  Irish  Acad., 
1848;  Reports  to  British  Axsoc.,  1850,  1851,  1852,  1853,  1854,  and  Trans.  Brit. 
Assoc,  1857-8;  The  Great  Neapolitan  Earthquake  of  1857,  8vo,  1862,  pt.  iii;  Phil. 
Trans.,  1862,  and  Amer.  Jour.  Sci.,  Ill,  v,  302. 


320  A    COOLING    PLANET. 

It  ought  to  be  mentioned  that  Professor  Wurtz,  as 
early  as  1866,  advanced  kindred  ideas.*  He  referred  to 
"the  tremendous  dynamic  agencies  whose  effects  of  up- 
heaval, subsidence,  disruption  and  displacement  we  find 
so  widely  manifest.  [These]  while  doubtless  themselves 
engendered  of  the  pent-up  heat-energy  of  the  interior, 
must  have  given  birth  to,  or  have  been  in  part  transmuted 
into,  heat-motion.  Hence  I  deduce  two  conclusions  of 
great  moment,  but  one  or  two  of  which  can  now  be  dwelt 
upon.  It  follows,  for  instance,  that  in  our  theoretical 
views  of  metamorphism,  we  are  by  no  means  of  necessity 
limited  for  our  essential  chemical  excitant,  merely  to  that 
portion  of  the  hypothecated  residual  cosmical  heat  which 
might  be  supposed  to  have  been  retained  by  the  emerging 
ocean  floor.  Neither  elevation  nor  subsidence  (both  neces- 
sarily accompanied  by  enormous  compression)  could  occur 
without  rise  of  temperature."  :  *  In  a  note  he  in- 

quires, "whether  the  general  rise  of  heat  represented  as 
found  on  descent  into  European  mines,  may  not  possibly 
admit  of  a  similar  explanation." 

Almost  simultaneously,  a  similar  conception  was  put 
forth  by  Mr.  George  L.  Vose.f  "The  enormous  pressure,'' 
he  says,  "generated  in  the  folding  of  masses  of  rocks  the 
depth  of  which  is  measured  by  miles,"  must  result  in 
great  mechanical  and  chemical  changes.  But  Wurtz  and 
Vose  merely  made  suggestions. 

Quite  independently  of  Mallet's  reasoning  and  appar- 
ently, also,  of  the  inconspicuous  suggestions  of  Wurtz  and 
Vose  (though  both  are  mentioned),  Professor  Joseph  Le 

*  In  a  paper  read  before  the  American  Association  at  its  Buffalo  meeting, 
and  afterward  published  in  the  Amer.  Jour,  of  Mining,  Jan.  25,  1868.  See 
extract  in  Amer.  Jour.  Set.,  Ill,  v,  385-6. 

tVose:  Orograpkic  Geology,  or  the  Oriff In  of  Mountains.  A  Review.  Bos- 
ton, 1866.  8vo.  136  pp. 


OROGENIC   FORCES.  321 

Conte,  of  California,  arrived  at  very  similar  conclusions,* 
and  like  Mallet  presented  them  with  adequate  exposition. 
He,  however,  combined  with  them  Hall's  conception  of 
copious  deposition  along  a  sinking-  sea-bottom.  He  went 
beyond  Hall,  at  the  same  time,  in  maintaining  a  local  ele- 
vation of  the  subsided  belt,  though  this  was  viewed  simply 
as  the  consequence  of  extensive  mashing  together,  and 
not  of  folding.  "According  to  my  view,"  he  says,  "  this 
yielding'  [to  tangential  thrust]  is  not  by  upbending  into 
an  arch,  leaving  a  hollow  space  beneath,  nor  such  an  arch 
filled  and  supported  by  an  interior  liquid,  but  a  mashing 
or  crushing  together  horizontally,  like  dough  or  plastic 
day,  with  foldings  of  the  strata,  and  an  upswelling  and 
thickening  of  the  whole  squeezed  mass.^  According  to 
Professor  Le  Conte's  views,  previously  explained,  the 
"upswelling"  must  be  accompanied  by  a  still  greater 
downswelling  to  counterpoise  the  elevation.  This  view  is 
also  maintained  by  Rev.  O.  Fisher,  who  says:  "The  pecul- 
iar arrangement  which  is  requisite  for  the  equilibrium  of 
a  disturbed  crust  resting  upon  a  heavier  fluid  substratum 
is,  that  for  every  subaerial  elevation  above  the  mean  sur- 
face there  must  be  a  corresponding  protuberance  dipping 
downwards  into  the  fluid  below;  and,  according  to  the 
relative  densities  which  we  have  assumed,  the  depth  of 
these  protuberances  must  be  about  ten  times  the  height  of 
the  elevations."!  The  writer  proceeds  to  state  that  this 
deep  protuberance  would  explain  the  relative  feeble  action 
of  mountains  on  the  pendulum,  since  the  mountain  and  its 
"roots"  would  be  less  dense  than  the  fluid  in  which  they 

*J.  Le  Conte,  A  Thtory  of  the  Formation  of  the  Great  Features  of  the 
Earth's  Surface,  Amer.  Jour.  Sci ,  III,  iv,  345  and  460,  Nov.  and  Dec.,  1872.  Sup- 
plementary Xote,  v,  156.  See  T.  S.  Hunt's  Criticisms  in  id.,  v.  264-70,  and  Le 
Conte's  Reply  in  id.,  \,  448,  June,  1873.  See  J.  D.  Dana's  remarks  in  id.,  v, 
26-8. 

t  Fisher:  Physics  of  the  Earth's  Crust,  286.  Prof.  James  Hall  had  previously 
said  of  mountains,  "There  is  doubtless  as  much  of  the  mass  below  the  level  of 
the  sea  as  above  it."—  Pal.  New  York,  iii,  Introduction. 
21 


322  A    COOLING    PLAXET. 

float;  but  he  states  elsewhere  that  "the  downward  protu- 
berances of  the  crust  into  the  fluid  substratum,  which  we 
have  termed  the  roots  of  the  mountains,  will  be  gradually 
melted,"  and  in  this  he  is  unquestionably  correct.  This 
must  cause  the  mountain  gradually  to  subside  to  the  com- 
mon level,  or  the  elevation  must  be  sustained  arch-like, 
with  the  creation  of  strains  in  the  contiguous  crust.  But 
as  the  mountains  have  not  subsided,  they  must,  therefore, 
consist  of  elevations  without- "roots,"  and  these  elevated 
masses  of  matter,  so  far  below  the  melting  temperature, 
must  be  denser  than  the  underlying  fluid.  Hence  they 
should  exert  an  excess  of  attraction  on  the  pendulum, 
instead  of  a  deficiency.  It  seems  more  probable  that  the 
elevations  are  sustained  partly  by  flotation,  and  partly  bv 
lateral  resistances  of  the  crust,  and  that  the  lighter  liquid 
fills  a  portion  of  the  arch,  giving  the  mountain  a  mean 
density  less  than  if  it  were  completely  solid  and  cold. 

The  final  crushing  together  of  a  geosynclinal,  forming 
a  mountain  protuberance,  constitutes  what  Professor  Dana 
has  styled  a  "synclinorium."  "In  such  a  process  of 
formation,"  he  says,  "elevation  by  direct  uplift  of  the 
underlying  crust  has  no  necessary  place.  The  attending 
plications  may  make  elevations  on  a  vast  scale,  and  so 
also  may  the  shoves  upward  along  the  lines  of  fracture, 
and  crushing  may  sometimes  add  to  the  effect;  but  eleva- 
tion from  an  upward  movement  of  the  downward  bent 
crust  is  only  an  incidental  concomitant,  if  it  occur  at  all."* 

In  connection  with  the  effects  of  crushing  pressure,  it 
is  interesting  to  recall  the  older  views  of  Sir  Charles 
Lyell:  "To  assume  that  any  set  of  strata  with  which  we 
are  acquainted  are  made  up  of  such  cohesive  and  un- 
yielding materials  as  to  be  able  to  resist  a  power  of  such 
stupendous  energv  [as  that  which  uplifted  the  coast  of 
Chili,  in  1822  and  1835]  if  its  direction,  instead  of  being 

*Dana,  Amer.  Journal  of  Science,  III,  v,  431. 


OROGENIC    FORCES.  323 

vertical,  happened  to  be  oblique  or  horizontal,  would  be 
extremely  rash.  But,  if  they  could  yield  to  a  sideway 
thrust,  even  in  a  slight  degree,  they  would  become 
squeezed  and  folded  to  any  amount,  if  subjected  for  a 
sufficient  number  of  times  to  the  repeated  action  of  the 
same  force.  *  *  *  Among  the  causes  of  lateral  pres- 
sure, the  expansion  by  heat  of  large  masses  of  solid  stone 
intervening  between  others  which  have  a  different  degree 
of  expansibility,  or  which  happen  not  to  have  their  tem- 
perature raised  at  the  same  time,  may  play  an  important 
part.  But  as  we  know  that  rocks  have  so  often  sunk  down 
thousands  of  feet  below  their  original  level,  we  can  hardly 
doubt  that  much  of  the  bending  of  pliant  strata,  and  the 
packing  of  the  same  into  smaller  spaces,  have  frequently 
been  occasioned  by  subsidence."  * 

5.  Statement  of  separate  Constructive  Conceptions 
relative  to  Mountain-making. — Having  presented  a  con- 
cise outline  of  the  principal  theoretical  systems  of  moun- 
tain-making, we  may  glance  back  and  eliminate  the  dis- 
tinct conceptions  which  have  risen  into  notice  from  time 
to  time,  and  most  of  which  have  some  valid  grounds  for 
recognition,  and  have  contributed  something  to  the  final 
theory.  They  may  be  enumerated  as  follows: 

(a)  A  liquid  nucleus  and  comparatively  thin  crust. 

Explains  internal  heat,  and  instability  of  earth's  surface. 
Objections.   Astronomical,  based  on  precession,  nutation,  tides, 

moon's  secular  acceleration ;  also  support  of  mountain  chains. 

[Probably  mostly  good.] 

(b)  A  solid  nucleus  and  a  plastic  zone,  either  continuous  (Fisher)  or 

interrupted  (W.  Hopkins). 

Explains  terrestrial  rigidity;  also,  in  part,  volcanic  and  seis- 
mic phenomena. 

*  Sir  C.  Lyell :  Principles  of  Geology,  6th  ed.,  1850,  pp.  167-8.  The  mashing 
process  is  recognized  by  Prof.  C.  H.  Hitchcock  in  his  discussion  of  the  White 
Mountains  (Geology  of  New  Hampshire,  i,  518-22,  1874).  He  also  finds  strata 
crumpled  in  detail  and  not  in  the  mass  and  all  alike,  as  represented  by  Rogers 
(id.,  ii,  114,  1877). 


324  A    COOLING    PLANET. 

(c)  Action  of  elastic  vapors  beneath  the  crust. 

Explains  volcanic  and  seismic  phenomena. 
Objection.    Inadequate  for  mountain  formation  and  mainten- 
ance.    [Good.] 

(d)  Secular  contraction  of  the  earth  more  rapid  in  the  nucleus,  thus 

causing  stresses  in  the  crust  (C.  Prevost). 

(e)  The  stresses  of  the  crust  find  relief  in  wrinkles  and  plications. 

Explains  elevations,  anticlinals  and  synclinals  with  or  without 
plications. 

Objections,  (aa)  Contraction  insufficient  (Button,  Fisher).     [To 
be  considered.]     (bb)  The  wrinkles  would  not  serve  as  germs 
of  elongated  mountain  ranges  (Button).     [Good.] 
(/)  The  stresses  of  the  crust  find  relief  in  mashing  together. 

Explains  heat  and  metamorphism  (Wurtz,  Mallet)  as  well  as 
plications  (Le  Conte). 

Objections,  (aa)  Would  not  develop  sufficient  heat  (Button). 
[To  be  considered.]  (bb)  The  "heat  would  not  be  sufficiently 
localized  (Button,  Fisher).  [Not  good.] 

(g)  The  mashing  together  sometimes  results  in  mountain-like  up- 
swellings  which  have  still  geater  down-swellings  to  counter- 
poise them  (Le  Conte,  Fisher). 

Explains  the  equilibrium  as  in  an  assumed  state  of  flotation, 
and  relieves  the  crust  of  strains  derived  from  their  weight  (if 
that  be  necessary). 

Objections,    (aa)  The  downward  protuberances  would  be  melted 
off.     [Good.]    (bb)  The  crust  can  stand  the  strain.     [Good.] 
(cc)  Pendulum  phenomena  show  the   mountains  deficient  in 
mass  or  density.     [Good.] 
(h)  A  residue  of  the  primitive  heat  remains  in  the  earth. 

Explains  internal  heat  and  accompanying  effects. 
(i)  Ascent  of  isogeothermal  planes  as  a  consequence  of  sedimentation 
(Babbage,  Herschel). 

Explains  metamorphism  of  sediments. 

Objection.    Boes  not  explain  metamorphism  in  strata  overlying 

strata  not  metamorphic.     [Good.] 

(/)  Excessive  sedimentation  along  geosyndinals —  these  being  either 
the  effects  (Hall)  or  the  cause  (Le  Conte)  of  the  excess  of  sedi- 
mentation. 

Explains  (aa)  deep  seated  metamorphism ;  (bb)  great  thick- 
ness and  fragmental  character  of  mountain  formations. 

Objection,     Insufficient,  as  giving  no  explanation  of  the  longi- 


OROGEXIC    FORCES.  325 

tudinal  extension  of  geosynclinals  or  of  the  causes  which  may 

produce  them  (ocean  currents  or  nuclear  contraction).  [Good.] 

[k)  Igneous  and  perhaps  aqueo-igneous  softening  along  a  deep  geo- 

synclinal. 
Explains  (aa)  existence  and  direction  of  a  line  of  weakness; 

(bb)  Local  metamorphism  and  vtilcanisra. 
(I)  Contraction  under  ocean  basins  developing  results  more  especially 

along  continental  shores  (Dana). 

Explains  the  border  location  of  mountain  chains  and  volca- 
noes. 
Objection.    The  ocean  bottoms  seem  to  have  been  also  the  seat 

of  development  of  contractional  results.     [Good.] 
(m)  Weight  of  ocean  would  add  something  to  landward  pressure 

resulting  from  (I), 
(n)  Contractions  under  extensive  plains  developing   results  along 

border  chains  of  mountains. 
Explains  (aa)  absence  of  plications  from  extensive  land  areas ; 

(bb)  The  border  location  of  mountain  chains. 
Objection  to  (m)  and  (n).     The  crust  would  not  slip,  even   if 

resting  on  a  liquid  (Button).     [Not  good.] 
(o)  Union  of  superheated  steam  with  a  zone  of  matter  beneath  the 

crust,  forming  a  state  of  igneo-aqueous  fusion  (Fisher). 
Explains  lateral  pressure  (as  the  author  of  it  thinks)   to  sup- 
ply alleged  deficiency  of  contractional  tension. 
Objections.    Energy  insufficient ;  action  too  local  and  too  little 

persistent.     [Good.] 

(p)  Tidal  action  on  the  primitive  forming  crust,  as  determinative  of 
lines  of  submeridional  structure  in  the  crust.  (See  this  work, 
Part  II,  Ch.  ii,  §  6,  4.) 

Explains  (aa)  existence  of  elongated  geosynclinals ;  (ii)  Their 
submeridional  direction — both  otherwise  entirely  unex- 
plained; (cc)  The  determination  of  the  oceanic  circulation  in 
definite  submeridional  currents,  should  these  be  appealed  to 
as  cause  of  submeridional  sedimentation  and  subsidence. 
(q)  Tidal  action  on  the  modern  earth  as  a  tributary  cause  of  vulcan- 
ism and  seismic  phenomena  —  acting  (aa)  By  the  production 
of  crushing  stresses;  (bb)  By  the  partial  relief  of  pressure  in 
places,  and  consequent  fusion  (King).  (See  this  work,  Part 
II,  Ch.  ii,  §  6,  6.) 

Explains  relations  of  these  phenomena  to  lunar  and  solar  posi- 
tions. 


326  A   COOLING    PLANET. 

6.  Final  Conception  of  Orogenic  History. —  This 
series  of  results,  worked  out  by  many  minds,  probably 
supplies  all  the  principal  elements  of  a  final  theory.  I 
shall,  therefore,  undertake  to  furnish  the  reader  with  a 
concise  digest  of  erogenic  history,  framed  of  those  con- 
ceptions which  seem  best  to  comport  with  observed  facts, 
and  with  the  operations  of  physical  forces. 

While  the  molten  earth  was  growing  through  the  pre- 
cipitation of  mineral  rains,  consolidation  began  at  the 
centre.  The  heat  of  the  solid  nucleus  was  exceedingly 
intense,  and  could  escape  only  by  conduction  to  the  envel- 
oping fluid,  and  thence  by  convection  to  the  terrestrial 
surface.  When  superficial  incrustation  began,  the  fluid 
portion  of  the  earth  had  fallen  nearly  to  the  temperature 
of  solidification.  The  forming  crust  having  a  tempera- 
ture little  below  that  of  the  underlying  liquid,  its  density 
was  less,  and  it  floated  on  the  liquid  magma;  though  later, 
when  its  mean  density  somewhat  exceeded  that  of  the 
magma,  its  own  rigidity  may  have  contributed  something 
to  its  support.  At  this  stage  the  moon  probably  was  much 
nearer  the  earth  than  at  present,  and  the  tidal  action  was 
intense.  While  in  the  formative  stage,  the  crust  was  im- 
pressed by  systems  of  submeridional  structure,  as  a  conse- 
quence of  the  tidal  lagging  which  gave  the  tidal  force  of 
the  moon  an  effective  tangential  component.  In  this 
action  was  implanted  that  bias  toward  meridionality  which 
has  revealed  itself  in  all  the  great  primitive  features  of 
the  earth's  crust.  As  a  consequence  of  this,  when  nuclear 
contraction  became  operative  in  the  wrinkling  of  the  crust, 
the  wrinkles  became  elongated  and  meridional;  and  the 
contractional  results  transverse  to  these  produced  only 
ruga?  and  knobs  in  the  main  wrinkles,  or  at  most,  short 
transverse  plications.  Probably,  to  some  extent  also,  the 
tendency  to  latitudinal  wrinkling  was  transformed,  over 
plains,  by  displacement  of  parts,  into  movements  conform- 


OROGENIC    FORCES.  327 

able  with  the  fundamental  and  predetermined  system  of 
wrinkles.  This  is  the  only  solution  of  a  difficulty  which 
Captain  Dutton  has  shrewdly  urged  against  the  contrac- 
tional  theory;  and  the  solution  seems  satisfactory. 

The  first  ocean  spread  itself  universally  over  the  wrink- 
ling crust.  There  were  ridges  and  valleys  beneath  the 
sea.  The  thickening  of  the  crust  experienced  an  accelera- 
tion. Copious  chemical  precipitates  were  thrown  down, 
and  mechanical  detritus  was  mingled  and  interstratified 
with  the  precipitates.  The  atmosphere  had  yielded  some- 
thing to  the  gathering  sediments,  so  that  the  crust  re- 
ceived more  than  it  gave.  At  a  later  stage  the  contrac- 
tion of  the  nucleus  enlarged  the  wrinkles,  and  the 
inequalities  of  the  sea  bottom  resulted  in  partial  emer- 
gences. Simple  synclinals  were  now  combining  into 
geosynclinals.  The  emergent  crust  was  powerfully  eroded, 
and  the  sediments  gathered  along  the  deeper  synclinals 
and  geosynclinals,  more  especially  if  these  were  located 
near  the  origin  of  the  sediments.  Meanwhile  the  nuclear 
contraction  continued  to  depress  the  geosynclinals  and 
elevate  the  geanticlinals.  If  water,  confined  beneath  the 
crust,  was  capable  of  uniting  with  the  molten  mass,  its 
progressive  escape  should  have  supplemented  the  possibly 
insufficient  results  of  simple  nuclear  cooling.  With  acces- 
sion of  sedimentary  layers  to  the  upper  surface  of  the 
crust,  corresponding  thicknesses  were  melted  from  the 
under  surface,  except  so  far  as  progressive  cooling  of  the 
earth,  or  diminished  conductivity  of  the  crust  permitted 
a  permanent  thickening  of  the  crust.  Thus,  step  by  step, 
with  the  emergence  of  the  geanticlinals,  proceeded  the 
depression  of  the  geosynclinals,  and  the  filling  of  certain 
of  them  with  sediments.  The  excess  of  sedimentation 
along  the  geosynclinals  caused  these  regions  to  experience 
most  the  melting  and  softening  action  of  the  heat  beneath. 
By  degrees  some  of  the  geosynclinals  became  composed 


328  A    COOLING   PLANET. 

of  softened  sediments  below,  and  fresh  and  imperfectly 
consolidated  sediments  above,  while  the  main  expanses  of 
the  crust  were  composed  of  older  and  more  rigid  materials. 
This  was  especially  true  of  the  geanticlinals.  The  geo- 
synclinals  were  therefore  zones  of  weakness  in  the  crust. 
With  continued  nuclear  shrinkage,  the  geosynclinals  con- 
tinued to  sink  and  the  geanticlinals  to  rise,  until  at  length 
the  lateral  thrust  of  a  geanticlinal  mass  became  too  great 
for  one  of  the  contiguous  geosynclinals  to  bear.  The 
geosynclinal  refused  to  be  further  depressed.  The  plastic 
mass  yielded  by  collapse.  The  result  was  an  enormous 
amount  of  crumpling,  plication  and  crushing  of  the  soft- 
ened strata,  with  the  development  of  additional  heat  and 
the  formation  of  faults  and  slides,  and  some  shoving  and 
over-slipping.  These  effects  would  be  greatest  along  the 
axis  of  the  geosynclinal.  While  the  geanticlinal  subsided 
to  some  extent,  the  geosynclinal  was  levelled  up  to  the  sea 
surface,  or  even  hundreds  or  thousands  of  feet  above  it. 
The  synclinorium  was  now  complete.  There  was  undoubt- 
edly some,  perhaps  great,  simultaneous  downward  swelling 
beneath  the  crumpling  geosynclinal,  but  while  the  emerged 
protuberance  was  becoming  cold  and  rigid,  the  submerged 
protuberance  gradually  disappeared.  Subsequent  sub- 
aerial  erosions  reduced  the  elevated  range  to  the  condition 
in  which  mountains  present  themselves  to  human  observa- 
tion, while  meantime  the  wasting  material  was  transported 
into  other  geosynclinals  whose  crises  had  not  yet  been 
reached. 

It  must  be  confessed  that  the  elevation  of  the  depressed 
geosynclinal  into  a  protuberance  of  mountain  magnitude 
presents  some  mechanical  difficulties  which  may  need  to  be 
further  considered.  Is  the  simple  work  of  crumpling, 
mashing  and  plication  a  sufficient  explanation  of  the  anti 
clinal  structure,  and  often  enormous  elevation,  which 
belong  to  mountain  phenomena  ?  M.  Faye  has  considered 


OROGEXIC   FORCES.  329 

the  influence  of  the  ocean's  bottom  temperature  upon  the 
thickness  of  the  suboceanic  crust,  and  he  argues  that  the 
subsidence  of  the  thickened  ocean  floor  would  react  be- 
neath the  continental  areas,  and  produce  all  the  phenomena 
ascribable  to  upheaval.  The  doctrine  of  wrinkling1  by 
lateral  pressure,  he  dismisses  entirely.  Now  it  can  be 
readily  admitted  that  such  subsidence  of  ocean  bottoms, 
additionally  loaded  by  the  weight  of  ocean  waters,  would 
result.  A  part  of  the  subsidence  would  be  compensated 
by  refusion  on  the  under  surface,  as  before  explained,  and 
a  residual  part  would  exert  a  mechanical  pressure  which 
would  react  under  the  land.  But  the  reaction  would  be 
generally  distributed.  It  might  thus  tend  to  upraise  broad 
continental  surfaces,  and  force  lava  through  the  weak 
places  of  the  crust.  But  the  greater  problem  in  geological 
mechanics  is  to  explain  the  special  and  local  elevatory 
phenomena  seen  in  mountains,  and  especially  the  great 
and  numerous  folds  which  have  come  into  existence  in  the 
principal  mountain  chains.  It  is  possible  that  the  great 
and  constant  pressure  exerted  by  the  thickened  ocean  bot- 
toms upon  the  fluid  understratum  may  determine  a  constant 
tendency  of  other  parts  of  the  crust  to  rise,  and  thus  con- 
tribute something  to  the  mechanical  agencies  which  pro- 
duce mountainous  elevations  on  occasion  of  the  collapse  of 
a  loaded  and  softened  geosynclinal. 

The  synclinorium  was  novv  more  an  arch  than  a  geosyn- 
clinal. While,  therefore,  nucleal  contraction  continued 
through  later  ages,  the  synclinorium  presented  a  form 
which  invited  further  uplifts.  It  became,  in  some  cases, 
a  true  geanticlinal  undergoing  supplementary  uplifts  from 
age  to  age,  or  sometimes  sinking  as  some  neighboring 
geosynclinal  attained  its  crisis 

Thus  the  crests  of  mountain  ranges  are  lines  of  fracture, 
and  often  of  prolonged  structural  weakness.  In  all  cases, 
excessive  erosion  has  thinned  and  weakened  the  rocky 


330  A    COOLING   PLANET. 

covering  of  the  plastic  magma  which  rises  into  the  moun- 
tain form  —  not,  indeed,  to  a  point  above  the  general  level 
of  the  continent,  but  to  a  point  quite  above  the  general 
level  of  the  under  side  of  the  crust  —  but  more  especially 
beneath  chains  of  mountains  covering  elevated  regions  of 
great  breadth,  as  the  Rocky  Mountains  and  the  Himalayan 
plateau,  *  and,  as  shown  to  some  extent,  in  the  section 
across  the  Alps,  Figure  52.  At  the  same  time,  the  actual 
thickness  of  the  solid  material  may  be  greater  in  moun- 
tains than  beneath  extensive  plains,  in  consequence  of  the 
increased  amount  of  radiating  surface.  Yet,  in  case  of 
reactions  of  the  underlying  molten  matter  against  the 
crust,  in  consequence  of  local  subsidence  somewhere,  or 
even  the  general  gravitative  pressure  of  the  crust,  or  some 
motion  resulting  from  tidal  action,  it  must  be  that  easiest 
vent,  save  in  case  of  linear  fractures,  would  be  found  along 
the  crests  of  mountain  ranges.  On  this  reasoning,  the 
highest  ranges  would  be  most  likely  to  offer  easiest  relief. 
So  volcanic  vents  should  be  expected  at  mountain  sum- 
mits as  well  as  along  lines  of  fracture  in  the  level  crust. 
At  the  same  time,  it  is  not  contended,  against  the  view  of 
Mr.  Poulett  Scrope,  that  very  many  —  mostly  moderate- 
sized —  volcanic  mountains  are  not  wholly  formed  from 
erupted  matters. 

In  this  view,  the  location  of  a  progressing  geosynclinal 
and  its  synclinorian  outcome  is  not  determined  by  the 
ocean.  The  geosynclinal  is  an  incident  of  the  general 
diversification  of  the  earth's  surface  contour,  and  the 
synclinorian  outcome  depends  on  the  proximity  of  a  source 

*This  conception  in  anticipated  by  Archdeacon  Pratt.  "  It  is  possible,"  he 
says,  "  that  the  superabundant  matter  in  mountain  regions  having  been  heaved 
up  from  below,  or  at  any  rate,  having  been  left  aloft  as  the  earth  contracted  its 
volume,  there  may  be  a  deficiency  of  matter  below  the  mountains,  which  would, 
under  certain  circumstances,  have  the  tendency  of  counteracting  their  effect  on 
the  plumb  line."  —  Pratt :  The  Figure  of  (he  Earth,  4th  ed.,  87.  Compare  also 
Airy,  Phil.  Trans.,  1855;  Pratt,  Phil.  Trans.,  1858-9,  and  the  results  of  Schmei- 
zer's  observations,  in  Monthly  Notices  Ast.  Soc.,  April,  1868. 


OROGENIC    FORCES.  331 

of  sediments.  Remote  from  shores,  geosynclinals  are  in 
progress  beneath  the  sea,  which  will  never  attain  synclin- 
orian  crises,  unless  some  revolution  provides  supplies  of 
sediments.  The  weight  of  the  ocean,  nevertheless,  must 
have  contributed  something-  to  the  tangential  thrust  which 
increased  the  elevation  of  a  synclinorium  after  it  acquired 
the  relations  of  a  geanticlinal.  This,  however,  it  seems  to 
me,  must,  in  some  cases,  have  been  exceeded  by  the  tan- 
gential thrust  transmitted  from  a  broad  continental  space 
not  undergoing  plication,  and  especially  such  a  space 
already  raised  into  a  geanticlinal.  The  inclination  of 
synclinorian  folds  toward  the  continent  would  result  rather 
from  the  continental  than  from  the  oceanic  thrust. 

Similarly,  the  border  situation  of  volcanic  ranges  is 
not  due  to  oceanic  action,  since  the  shore-line  and  the  vol- 
canic range  have  been  determined  simultaneously  by  the 
position  of  a  completed  synclinorium.  The  ocean  being 
in  proximity  to  the  volcano,  its  water  naturally  finds  access 
to  the  media  destined  to  be  ejected,  and  even  aids  in  their 
ejection;  but  it  is  an  error  to  suppose  that  elastic  vapors 
are  capable  of  doing  the  greater  work  of  volcanic  and 
seismic  activity. 

The  progress  of  the  geosynclinal  would  be  attended  by 
the  slow  metamorphism  of  the  deep  sediments,  through 
the  agency  of  internal  heat  and  water.  The  synclinorian 
crisis  would  produce  plications  and  elevations,  together 
with  additional  heat  and  further  metamorphism.  The 
completion  of  the  synclinorium  would  be  followed  by 
completed  crystallization  and  consolidation.  Later  geanti- 
clinal action  would  bring  the  mountain  chain  to  its  maxi- 
mum elevation.  In  still  later  periods,  this  elevation  would 
be  reduced  by  erosion  and  by  subsidence  resulting  from 
strains  in  the  contiguous  crust,  due  to  the  weight  of  the 
mountain-mass. 

7.   Analytical  Conspectus  of  Oroyenic  Speculations. — 


332  A    COOLING    PLANET. 

To  render  as  clear  as  possible  to  the  general  reader  the  re- 
lations of  the  various  theories  of  mountain-making  which 
have  been  passed  in  review,  I  introduce  here  an  analytical 
exhibit  in  which  the  different  erogenic  conceptions  are 
ranged  in  due  order  of  subordination;  and  some  effort  is 
made  to  annex  to  the  several  characteristic  conceptions  of 
different  investigators  the  views  which  they  have  associated 
in  their  systems  with  the  conceptions  contributed  by  them- 
selves. 

I.  Reaction  of  heated  elastic  vapors  beneath  the  crust. 

The  vapors  generated  from  matter  admitted  from 
above, 

With  a  thin  terrestrial  crust, DAVY,  etc. 

With  a  solid  earth  and  local  lakes  of  lava,   .     .     .    HOPKIXS. 
The  vapors  generated  beneath  the  crust  in  a  liquid 

or  plastic   zone,   and   causing,   in  'fissures,   lateral 

compression,  crushing  and  plications,     ....       FISHER. 

II.  Expansion  (by  heat)  of  subsided  sediments,      ...  BABBAUE. 

III.  Depression  of  thickened  crust  beneath  oceans,  and 
reaction  on  continents,     .......--         FAYE. 

IV.  Contractional  mechanism  (C.  Provost,  E.  de  Beau- 
mont, Sedgwick,  etc.). 

Meridionality  unexplained. 
Fluidity  primitive. 

The  earth's    nucleus    fluid  (Humboldt,  v.    Buch, 
etc.),     ..........        .      OL.D  THEORY. 

Fluidity  or  plasticity  limited  to  a  zone  more  or  less 

continuous, 

Without  intervention  of  geosynclinals,  and  with- 
out mashing  together.     Wrinkling  alone. 
Plications  the  accompaniment  of  gen-  j       KEFERSTEIX, 

eral  contraction, (  HERSCHEI.,  etc. 

Plications   the   result  of   subsidence  of   fold; 
thickened  strata  resulting  from  erosion  of 
granitic  nucleus  of   mountain,    ....  WHITNEY. 
With  the  intervention  of  geosynclinals  (Hall). 
Subsidence  caused  by  weight  of  sediment  s  (Hall), 
and  deep-seated  condensation  (Hunt);  moun- 
tains only  relief  features  of   eroded  conti- 


OROGENIC    FORCES. 


333 


nents,    in    earlier  times  somehow  elevated 
(Buffon,  tie  Montlosier,  Lesley);  subsidence 
resulting  in    motion   or   fermentation   and 
pressure,  which,  with  moderate  accession  of 
heat  from  below,  cause  metamorphism,  etc., 
(Hall)  [Continental  elevation  not  explained]. 
Subsidence  the  principal  cause  of  the  corru- 
gations of  the  earth's  strata,     ....         HALL. 
Subsidence  not  the  principal  cause  of  the 
earth's  corrugations,  but  only  of  their  po- 
sition and  direction.      A  zone  of   plastic 
material  in  aqueo-igneous  fusion  beneath 
the  crust,  augmented  by  subsidence  caus- 
ing vulcanic  phenomena  and  softening  of 
deep    crust,   forming    lines  of    weakness 
along  which  are  developed  results  of  con- 
traction of   the  earth    and    of   the  deep 

crust  itself, HUNT. 

Subsidence  caused  progressively  by  lithifica- 
tion  below,  and  increasing  density,  and  after- 
ward aqueo-igneous  fusion,  metamorphism 
and  slaty  cleavage,  and  determination  of  line 
of  weakness  and  yielding  to  horizontal  pres- 
sure; no  elevation  except  by  crushing  to- 
gether, with  upswelling  and  corresponding 
down  swelling  Heat  partly  primitive, 
partly  of  chemical  origin.  Continents  and 
ocean  basins  resulting  from  unequal  radial 
contraction.  [No  explanation  of  elevation 

without  plications.] __LE  CONTE. 

Subsidence  an  incident  of  general  contraction. 
Copious  sedimentation  along  geosynclinals. 
Finally,  plications,  shoving  along  fractures, 
and  some  crushing,  resulting  in  elevation. 
Geanticlinal  elevations  discriminated.  In- 
creased pressure  from  the  side  of  the  great 

oceans, _....         DANA. 

Fluidity  not  necessarily  primitive  (Wurtz,  Mallet). 
Fluidity  caused  by  contractional  evolution  of  heat. 

Heat  resulting  from  pressure  and  chemical  action.          VOSE. 
Heat  resulting  from  crushing  of  earth's  crust, 


334  A    COOLING    PLANET. 

with  accompanying  thermal   and  mechanical 
consequences,   and  variations   in   rate   of    in- 
crease of  hypogeal  temperature,     ....     MALLET, 
Meridionality  of  crust-structures  due  to  primitive  tidal 
action.     Fluidity  contractional,  tidal,   and   perhaps 
primitive.   Sedimentation  along  geosynclinals  located 
in  position  and  direction  by  the  lunar  tidal  actions  on 
the  primitive  earth ;  mashing  together  with  plications 
and  metamorphism ;    consequent   elevation  and  cor- 
responding depression;  the  depression  progressively 
removed  by  re-fusion,  and  the  mountain  standing- 
somewhat  arch-like,  with  a  molten  or  highly  heated 
core  and  lower  density;    weight  of    mountain   pro- 
ducing strains  in  the  crust,  mountain  consequently 
undergoing  secular  subsidence.      Geanticlinal  eleva- 
tions  produced   by  lateral   pressure   resulting   from 
contraction,    and    secondarily,  in  part,  from  weight 
of  mountains.      Submarine  geosynclinals  and  gean- 
ticlinals  as  well  as  continental,  and  hence  no  greater 
contractional  pressure  from  oceanic  side,  ...    THIS  WORK. 
Various  other  suggestions  have  been  made  during  the 
history   of   geological    speculation,    most    of    which    have 
never  gained  any  particular  repute.     M.  de  Boucheporn 
conjectured  that  each  geological  revolution  was  the  result 
of  a  sudden  change  in  the  direction  of  the  earth's  axis, 
caused  by  collision  with  a  comet.     The  shock  before  the 
last,  for  instance,  left  the  equator  in  the  position  of  the 
Andes  chain;  the  last  left  it  in  the  actual  position;  the 
next    will    produce    still    another    revolution.     Geologists 
have  also  considered  the  possibility  of  a  change  in  the  axis 
resulting  from  a  redistribution  of  the  land  and  water  — 
but  this  more  especially  to  explain  vicissitudes  of  climate.* 

*  Sir  Wm.  Thomson,  Brit.  Assoc.  Rep.,  1876,  Part  II,  p.  11 ;  Traits.  Geol.  Soc., 
Glasgow,  iv,  313;  Haughton,  Proc.  Roy.  Soc.,  xxvi,  51,  April  4,  1878;  Nature, 
xviii,  260-8;  G.  H.  Darwin,  Trans.  Hoy.  Soc.,  clxvii,  Part  I;  I.  F.  Twisden, 
Quar.  Jour.  Geol.  Soc.,  Feb.,  1878;  Airy,  Athenaeum,  22  Sep.,  1809;  Croll,  Geol. 
Mag.,  Sep..  1878;  E.  Hill,  Geol.  Mag.,  June,  1878.  See  also  Laplace:  Systeme  du 
Monde,  ed.  1824,  p  392.  For  some  recent  views  on  the  tendency  of  the  earth's 
crust  to  subside  under  pressure,  see  J.  Starkie  Gardner,  in  Nature,  xxviii,  323-7, 
August  2,  1883. 


THE    PLANETARY    CRUST.  335 

This  speculation,  however,  generally  leaves  the  cause  of 
the  change,  even  if  real,  unaccounted  for.  Rev.  O.  Fisher 
suggested,  on  the  strength  of  Darwin's  theory  of  the 
separation  of  the  moon  from  the  plastic  earth,  that  perhaps 
the  ocean  basin  represents  the  cavity  left  on  that  occasion.* 

§  11.   UNEQUAL  THICKNESS  OF  THE  PLANETARY  CRUST. 

Let  us  recur  for  a  moment  to  the  physical  conditions 
coexisting  with  the  mountain  masses  whose  origin  we  have 
sought  to  discover.  A\rith  the  progressive  development  of 
wrinkles,  groups  of  wrinkles  and  continental  expanses,  a 
gradual  differentiation  of  different  regions  of  the  planetary 
surface  would  be  in  progress.  This  would  produce  that 
diversification  of  conditions  which  would  be  attended  by 
an  ever-increasing  diversification  in  the  organic  aspects  of 
land  and  water — since,  as  will  be  remembered,  this  dis- 
cussion concerns  for  the  present  a  planet  upon  which  water 
has  existence.  As  we  can  hardly  suppose  conditions  on 
such  a  planet,  under  which  no  molecular  disintegration 
would  take  place,  we  must  conclude  that  the  emerged  and 
uplifted  folds  and  synclinorian  arches  of  the  crust  would 
be  exposed  to  perpetual  denudation;  and  this  would  ulti- 
mately thin  the  crust  along  the  axes  of  the  great  folds  and 
arches  to  such  an  extent  that  the  mountains  of  anticlinal 
structure  would  tend  to  become  mere  shells  filled  with 
molten  matter,  or  at  least  matter  of  a  very  high  tempera- 
ture. This  condition  of  mountain  masses  would  of  course 
impart  to  them  a  density  less  than  that  of  the  average 
crust  beneath  the  plains.  As  another  result,  the  mountain 
crests  would  be  lines  of  great  relative  weakness;  and 
hence  any  pressure  acting  from  beneath  would  be  most 
likely  to  find  relief  through  mountain  summits.  At  the 
same  time,  the  heated  matter  within  and  beneath  the 

*  O.  Fisher,  Nature,  xxv,  343-4. 


336  A    COOLING    PLANET. 

mountain  would  be  exposed  to  a  freer  radiation  than  the 
matter  beneath  the  plain,  and  for  this  reason  the  solid  crust 
should  be  able  to  thicken  with  a  pace  somewhat  equal  to 
the  wastage  by  denudation.  But  if  tidal  movements  of 
the  crust,  or  currents  or  tidal  swells  in  the  subjacent  liquid 
should  create  a  predisposition  in  the  molten  matter  to  seek 
and  frequent  the  spaces  under  the  mountain  anticlinals, 
this  cause  might  interfere  with  the  thickening  due  to  the 
unusual  exposure  of  a  mountain  convexity  to  the  process 
of  radiation,  and  thus  preserve  the  unusual  thinness  which 
tends  to  result  from  surface  erosions. 

Now,  tidal  influences  would  tend  to  cause  currents  in 
the  molten  interior.  As  soon  as  the  crust  shall  come  to 
possess  any  sensible  rigidity,  the  height  to  which  the  tidal 
swell  would  rise  would  be  somewhat  less  than  that  which 
the  same  attraction  would  produce  in  a  fluid.  The  under- 
lying fluid  would,  therefore,  press  against  the  under  side  of 
the  tidal  arch.  If  at  such  a  time,  a  vent  should  exist  or 
be  opened  in  the  arch,  the  fluid  would  escape,  and  this 
would  determine  currents  toward  the  place  of  outlet.  Such 
vents  would  be  most  likely  to  be  opened  when  the  crest  of 
the  tidal  swell  should  coincide  with  the  line  of  weakness 
along  a  mountain  anticlinal.  The  result  would  be  an  influx 
of  molten  matter  from  all  directions;  and  the  effect  of  this 
would  be  to  prevent  thickening  of  the  mountain  fold,  if  it 
did  not  actually  reduce  its  thickness.  Further  than  this, 
the  very  existence  of  permanent  swells  or  folds  in  the 
crust  would  be  the  condition  of  translatory  movements  in 
the  underlying  liquid.  The  partial  rigidity  of  the  crust, 
as  just  stated,  would  cause  the  underlying  liquid  to  press 
against  it.  This  pressure  would  be  transferred  westward 
from  point  to  point.  There  would  be  a  time  when  the 
apex  of  the  tidal  swell  would  be  near  the  base  of  an  anti- 
clinal fold.  It  is,  therefore,  obvious  that  the  pressure  in 
this  situation  would  initiate  an  actual  motion  of  the  fluid 


THE    PLANETARY    CRUST.  337 

in  the  direction  of  relief  —  that  is,  toward  the  crest  of  the 
anticlinal.  It  is  quite  true  that  the  tidal  pressure  would 
reach  and  pass  the  anticlinal  before  the  relief  which  the 
latter  would  afford  could  be  fully  realized.  But  the  fluid 
would  have  received  an  impulse  toward  the  anticlinal 
which  would  live  for  some  time  after  the  tide  had  passed. 
This  impulse  would  be  renewed  at  every  semi-rotation  of 
the  planet  perpetually.  I  imagine  that  the  consequence 
would  be  the  perpetual  transference  of  more  highly  heated 
matter  to  the  region  under  the  fold,  and  the  prevention  of 
normal  increase  of  thickness. 

On  the  contrary,  some  causes  may  exist  for  a  greater 
than  average  thickness  under  masses  of  ocean  waters.  In 
the  first  place,  the  continual  accumulation  of  sediments 
would  not  be  fully  offset  by  fusion  upon  the  under  side  of 
the  crust;  nor  even  to  such  extent  as  the  secular  cooling 
of  the  planet  and  thickening  of  the  crust  would  imply. 
The  accumulation  takes  the  initiative,  and  the  removal 
from  below  is  the  reaction.  The  time  which  separates  the 
action  and  the  reaction  would  give  opportunity  for  some 
uncompensated  accumulation.  But,  in  the  second  place, 
the  normal  circulation  of  oceanic  waters  would  keep  a 
stratum  of  nearly  ice-cold  water  upon  the  bottom,  spread 
over  the  ocean's  floor.  This  is  a  colder  temperature  than 
the  mean  temperature  of  the  atmosphere  in  any  except 
subarctic  and  arctic  regions.  The  planetary  crust,  there- 
fore, is  exposed  to  a  more  effective  cooling  temperature 
under  the  oceans  than  on  the  land.  Finally,  the  water  in 
contact  with  the  crust  under  the  oceans  is  a  better  conduc- 
tor of  heat  than  the  atmosphere  in  contact  with  the  land. 
These  three  reasons  would  conspire  to  produce  a  thicker 
crust  under  the  oceans  than  under  the  continental  surfaces. 
23 


CHAPTER  III. 

SPECIAL  PLANETOLOGY, 

OB     PRESENT     CONDITION     AND     COSMOGONIC     HISTORY    OF 
THE    PLANETARY    BODIES    OF    OUR    SYSTEM. 

§  1.    THE  EARTH. 

Each  orb  has  had  its  history.    For  ours, 

It  blazed  and  steamed,  cooled  and  contracted,  till, 

Tired  of  mere  vaporing  within  the  grasp 

Of  ruthless  condensation,  it  assumed 

Its  present  form,  proportions,  magnitude  — 

Our  tidy  ball,  axled  eight  thousand  miles.— DAVID  MASSON. 

ACCORDING  to  nebular  theory,  all  the  members  of 
-£j-  our  system  must  pass  sooner  or  later,  through  the 
same  succession  of  stages.  The  circumstances  of  different 
planetary  bodies,  however,  have  differed  widely,  and  the 
details  of  their  evolution  have  assumed  very  diversified 
aspects.  The  principal  factors  concerned  in  the  special 
histories  of  these  bodies,  so  far  as  we  can  judge,  are  mass, 
volume,  distance  from  the  sun,  age,  and  magnitude  of  the 
tidal  actions  exerted  upon  them.  Connected  with  mass 
and  volume  are  the  quantity  of  atmosphere  and  its  density 
on  the  planetary  surface,  and  hence  the  temperature  of 
steam  formation  and  the  thermal  effect  of  solar  radiation. 
Let  us  consider  attentively  the  probable  influences  of  the 
diversified  conditions  of  planetary  existence  in  our  system, 
beginning  with  those  bodies  most  accessible  to  physical 
inquiry. 

Our  planetary  home  occupies  the  temperate  zone  of  the 
solar  system.  It  presents  us  also  an  array  of  facts  from 
which  we  may  verify  many  of  the  conclusions  deductively 


THE   EAETH.  339 

reached  from  physical  principles.  We  have  here  innu- 
merable surface  indications  of  a  former  high  temperature 
upon  the  exterior  of  the  globe.  Numerous  other  phenomena 
testify  to  the  perpetuation  or  perpetual  production  of  a  high 
temperature  at  all  considerable  depths  beneath  the  sur- 
face. The  records  of  extinct  life  testify  to  a  progressive 
subsidence  of  temperature  during  long  past  ages,  and  pos- 
sibly also,  to  a  diminution  of  solar  heat;  and  wide-spread 
sheets  of  marine  sediments  declare  the  former  existence  of 
a  universal  ocean. 

1.  Condition  of  the  Earth's  Interior. —  That  great 
heat  exists  within  the  earth  is  abundantly  demonstrated; 
but  the  condition  of  the  general  interior  has  been  much 
discussed.  Sir  Humphrey  Davy,*  Daubeneyf  and  others 
maintained  that  chemical  action  was  adequate  to  produce 
the  thermal,  dislocating  and  orographic  phenomena 
which  have  been  observed.  Mr.  F.  M.  Endlich  has  re- 
cently detailed  remarkable  thermal  and  explosive  mani- 
festations on  the  island  of  Dominica,  which  he  thinks 
clearly  attributable  to  chemical  action,  but  which  so  much 
resemble  volcanic  action  as  to  give  good  countenance  to 
Davy's  theory. J 

An  opinion  for  a  long  time  more  widely  accepted,  was 
that  which  conceived  the  great  interior  mass  of  the  earth 
as  existing  in  a  molten  state,  and  the  solid  portion  as  con- 
stituting a  mere  film  commonly  designated  the  crust.  This 
conception  has  come  down  from  Descartes  §  and  Leibnitz,  | 
and  until  recently,  has  been  very  widely  accepted. 

*Davy,  Phil.  Trans.,  1858,  1832. 

tDaubeney,  Jameson's  Edinb.  New  Phil.  Jour.,  liii,  and  Encyc.  Met.,  pt.  40. 
See  also  Ennis:  Origin  of  the  Stars,  and  Studer:  Geologic  der  Schweiz. 

i  Endlich,  The  American  Naturalist,  xiv,  761-72,  November,  1880. 

§  Descartes :  Principes  de  la  Philosophic,  1644,  pt.  iv,  §§  2,  44,  72. 

||  Leibnitz:  Ada  Eruditornm,  January,  1693,  and  Protogcea,  1749.  Compare 
also  Newton:  Principia  Mathematica  Philosophice  Naturalis,  1667,  and  Bnffon: 
Epoques  de  la  Nature,  1778.  For  statement  of  Leibnitz'  speculations,  see  Part 
IV,  §4. 


340  SPECIAL   PLANETOLOGY. 

The  whole  doctrine  of  a  molten  interior  was  objected 
to  by  Professor  W.  Hopkins*  on  the  ground  that  the 
phenomena  of  precession  and  nutation  could  not  be  what 
they  are  unless  the  earth  were  solid,  or  had,  at  least,  a 
crust  from  800  to  1,000  miles  in  thickness — sufficiently 
thick  to  give  it  a  high  degree  of  rigidity.  The  idea  was 
taken  up  from  new  considerations  and  reinforced  by  Sir 
William  Thomson  in  several  remarkable  scientific  me- 
moirs,! *n  which  he  distinctly  maintained  the  theory  of  a 
solid  globe;  though  he  claimed  that  the  solidity  of  the 
central  portion  may  be  the  result  of  pressure  of  the  super- 
incumbent portions.  Geologists  and  physicists  generally 
have  shown  a  disposition  to  acquiesce  in  the  judgment  of 
such  mathematicians.  It  does  not  appear,  however,  to 
the  writer  that  the  astronomical  considerations  are  con- 
clusive, since  whatever  external  attractions  are  exerted  on 
the  protuberant  crust  about  the  equator  would  be  almost 
equally  felt  by  the  protuberant  magma  underneath  the 
crust,  and  the  solid  and  liquid  portions  of  the  equatorial 
protuberance  would  tend  to  move  consentaneously.  It  is 
quite  true  that  the  crust-protuberance  would  be  slightly 
more  affected  than  the  molten  protuberance  beneath  it, 
both  because  it  would  be  slightly  nearer  the  attracting 
body,  and  because  the  eccentricity  of  successively  interior 
zones  may  be  regarded  as  successively  less.  Still,  if  the 
thickness  of  the  crust  is  held  to  be  but  a  few  miles,  these 
differences  must  be  almost  too  slight  to  enter  into  calcula- 
tion, and  would  be  mostly  concealed  by  the  presumable 
viscosity  of  the  molten  magma,  and  the  friction  upon 
itself  and  the  enveloping  crust.  The  defects  in  the  argu- 

*  Trans.  Roy.  Soc.,  18:36,  p.  382;  1838,  p.  38;  1840,  p.  193;  1842,  p.  48.  His 
three  memoirs  for  ia39, 1840  and  1842  embrace  a  complete  investigation  of  the 
subject.  See,  also,  On  the  Geological  Theories  of  Elevation  and  Earthquakes  in 
Brit.  Assoc.  Rep.,  1847,  pp.  33-93;  also  Quar.Jour.  Geol.  Soc.,  viii,  50. 

tSir  W.  Thomson,  Trans.  Roy.  Soc.,  May,  1862;  Thomson  and  Tail:  Nat. 
Philosophy,  vol.  i. 


THE   EARTH.  341 

ment  for  internal  solidity,  based  on  the  phenomena  of 
precession  and  nutation,  were  pointed  out  by  Delaunay,* 
who  maintained  that  the  motions  of  precession  and  nuta- 
tion are  so  slow  that  the  internal  fluid,  in  consequence  of 
friction  and  viscosity,  would  partake  precisely  of  the  mo- 
tion of  the  crust.  Archdeacon  Pratt,  however,  dissents 
from  Delaunay, f  while  General  Barnard  holds  that  Hop- 
kins' results  are  vitiated  by  an  oversight.  J  The  problem 
has  also  been  discussed  by  Hennessey  and  Haughton.§ 
Sir  William  Thomson  informs  us  also  that  Professor  New- 
comb  does  not  admit  the  validity  of  the  reasoning  from 
precession  and  nutation, |  and  that  Newcomb's  doubts  led 
him  to  a  reinvestigation  of  the  problem,  the  result  of 
which  was  a  confirmation  of  the  doctrine  of  internal  solid- 
ity, with  some  qualifications  in  the  actual  case.  In  a  still 
later  utterance,  however,  Sir  William  Thomson  admits 
that  "the  arguments  derived  from  the  phenomena  of  pre- 
cession and  nutation  present  considerable  difficulties,  and, 
indeed,  do  not  afford  us,  at  the  present  time,  a  decisive 
answer.  *[  In  reference  to  this  particular  argument  for 
internal  solidity  we  may,  therefore,  unite  with  Rev.  O. 
Fisher  in  pronouncing  it  obsolete.** 

This,  however,  is  not  to  abandon  the  theory  of  internal 
solidity.  There  still  remains  a  body  of  considerations 
lying  in  the  border  ground  between  terrestrial  and  cosmi- 
cal  physics,  which  furnish  evidence  not  yet  invalidated, 

*  Comptes  Rendus,  1868;  translated  in  Geological  Magazine,  v,  507,  Nov., 
1868.  Also  Cours  Elementaire  cT  Astronomie,  643,  644. 

t  Pratt:  Figure  of  the  Earth,  4th  ed.,  1&3-6. 

i  Barnard,  Problems  of  Rotary  Motion,  Smithsonian  Contrib.,  No.  240, 
New  Addendum,  p.  42,  vol.  xix,  1871. 

§  Hennessey.  Phil.  Trans.,  1851,545;  Trans.  Roy.  Irish  Acad.,  1852;  Phil. 
Mag.,  Sept.,  1860. 

1  Sir  W.  Thomson,  Glasgow  Address,  Brit.  Assoc.,  1876,  Amer.  Jour.  Sci., 
Ill,  xii,  342. 

^  Sir  W.  Thomson,  Trans.  Geol.  Soc.,  Glasgow,  1879,  p.  48. 

**Rev.  O.  Fisher:  Physics  of  the  Earth's  Crust,  London,  1881,  p.  22.  This  is 
a  very  important  work. 


342  SPECIAL   PLANETOLOGY. 

that  the  earth  must  possess  a  high  degree  of  rigidity.  These 
considerations  are  supplied  by  the  phenomena  and  the 
philosophy  of  tides;  and  have  been  likewise  profoundly 
discussed  by  Sir  William  Thomson  *  and  Archdeacon 
Pratt.f  Were  the  terrestrial  crust  so  yielding  as  to  offer 
only  fluid  resistance  to  tidal  action,  it  would  rise  and  sink 
with  the  waters  of  the  sea,  so  that  the  ocean  tides  would 
produce  no  increase  or  diminution  of  depth.:):  If,  on  the 
contrary,  the  earth  were  perfectly  rigid,  the  whole  tidal 
action  would  be  developed  in  the  waters,  and  the  tides 
would  increase  the  depth  to  a  certain  extent.  The  amount 
of  this  increase  of  depth  has  been  calculated,  but  tidal  ob- 
servations have  not  yet  been  sufficiently  exact  to  deter- 
mine how  the  facts  correspond  with  the  theory  of  a 
perfectly  rigid  globe.  The  actual  tide,  however,  seems  to 
be  somewhat  less  than  the  theoretical  tide,  and  this  affords 
some  inductive  ground  for  the  theory  that  while  the  earth 
possesses  a  high  degree  of  rigidity  it  is  not  perfectly 
rigid.  Perfect  rigidity  would  not,  indeed,  exist  even  in  a 
globe  of  steel.  Sir  William  Thomson  has  shown  that  if 
the  earth  were  as  rigid  as  steel  the  amount  of  its  yielding 
to  tidal  action  would  be  such  that  the  ocean  tides  would 
be  only  two-thirds  of  what  they  would  be  with  perfect 
terrestrial  rigidity;§  if  the  earth  were  no  more  rigid  than 
glass,  the  relative  rise  of  the  ocean  tide  would  give  a 
depth  only  two-fifths  ||  of  that  on  a  perfectly  rigid  globe. 
Now  the  theoretical  height  of  the  tides  has  been  calcu- 
lated on  the  assumption  of  perfect  terrestrial  rigidity;  and 
it  is  incredible  that  the  actual  tides  should  be  only  two- 
thirds  of  the  requirement  of  theory  without  a  discovery 

*  Sir  W.  Thomson,  Phil.  Trans.,  1863,  p.  574;  Trans.  Geol.  Soc.,  Glasgow,  vi, 
48-9. 

t  Pratt:  Figure  of  the  Earth.  4th  ed.,  138-40. 

JSee  explanations,  Pt.  II,  chap,  ii,  §  6,  1. 

§  Archdeacon  Pratt  brings  out  the  result  "three-fifths." 

|  According  to  Pratt,  "  two-ninths/' 


THE   EARTH.  343 

of  the  discrepancy  by  means  of  observation.  The  whole 
earth  must,  therefore,  be  more  rigid  than  glass.  Such  a 
degree  of  rigidity  could  not  be  imparted  by  a  rocky  crust 
having  a  thickness  of  fifty  or  a  hundred  or  five  hundred 
miles.  Such  rigidity  may  well  be  conceived  to  result 
from  the  general  solidification  of  the  interior.  This,  how- 
ever, as  before  explained,  would  not  result  from  the  law 
which  correlates  solidifying  point  with  amount  of  pressure 
sustained. 

Mr.  G.  H.  Darwin,  in  the  course  of  his  researches  on 
the  cosmic  influence  of  tides,  has  incidentally  arrived  at 
confirmations  of  the  doctrine  of  internal  rigidity.  He 
has  shown  that  the  diurnal  and  semi-diurnal  bodily  or 
deformative  tides  produced  in  the  earth  by  the  moon  are 
not  sufficient  to  reveal  their  existence  in  the  secular  accel- 
eration of  the  moon's  mean  motion,  though  Sir  William 
Thomson  had  assumed  the  two  phenomena  reciprocally 
connected.*  The  support  of  mountain  masses  implies  also 
a  high  degree  of  rigidity.  Mr.  Darwin  has  shown  that 
either  the  materials  of  the  earth  have  about  the  strength 
of  granite,  at  1,000  miles  from  the  surface,  or  they  have  a 
much  greater  strength  nearer  the  surface. f 

Still  more  recently  Mr.  (now  Professor)  G.  H.  Darwin 
has  subjected  the  rigidity  of  the  earth  to  a  new  discus- 
sion. J  Abandoning  the  study  of  diurnal  and  semi-diurnal 
tides  as  too  much  influenced  by  meteorological  accidents, 
he  fixes  on  the  lunar  fortnightly  declinational  tide,  and 
the  lunar  monthly  elliptic  tide.  Using  for  data  the  Tidal 
Reports  of  the  British  Association,  and  the  Indian  Tide 
Tables,  for  a  period  of  thirty-three  years,  at  fourteen  dif- 
ferent ports  in  England,  France  and  India,  and  taking  due 
account  of  the  interferences  of  the  land  masses  of  the 

*  G.  H.  Darwin,  Proc.  Brit.  Assoc.,  Dublin,  1878,  Nature,  xviii,  581. 
tG.  H.  Darwin,  Proc.  Roy.  Soc.,  June  16, 1881. 

$  Paper  read  at  the  British  Association,  Southampton  meeting,  1882.  Pub- 
lished in  Nature,  xxvii,  22-3,  Nov.  2,  1882. 


344  SPECIAL    PL  A  FETOLOGY. 

earth,  he  finds,  after  a  most  laborious  calculation,  that, 
taking-  all  the  observations  together,  there  "seems  to  be 
some  evidence  of  a  tidal  yielding  of  the  earth's  mass," 
but  that  "the  effective  rigidity  of  the  whole  earth  is  about 
equal  to  that  of  steel."  If  only  the  Indian  observations 
are  used  for  a  period  of  forty-eight  years,  the  rigidity 
appears  to  be  somewhat  greater.  "  On  the  whole,  we  may 
fairly  conclude,"  he  says,  "that,  while  there  is  some  evi- 
dence of  a  tidal  yielding  of  the  earth's  mass,  that  yielding 
is  certainly  small,  and  the  effective  rigidity  is  at  least  as 
great  as  steel."  * 

Admitting  the  general  solidity  of  the  earth,  it  is  still 
evident  that  large  supplies  of  molten  matter  exist  within. 
Now  we  may  rationally  conceive  three  independent  causes 
of  a  state  of  liquefaction  at  some  depth  beneath  the 
surface. 

(1.)  There  may  be  a  zone  too  deep  for  solidification  by 
cooling  and  too  shallow  for  solidification  by  pressure.  Or, 
in  more  exact  terms,  the  downward  increase  of  terrestrial 
temperature  for  a  certain  distance  may  be  more  rapid  than 
the  rise  of  that  function  of  pressure  which  produces 
solidification;  but  at  greater  distances  from  the  surface, 
less  rapid  than  the  rise  of  the  same  function.  During  the 
first  interval  the  pressure  will  not  be  sufficient  to  produce 
solidification  at  the  temperature  existing;  but  during  the 
deeper  descent  the  pressure  will  be  enough  or  more  than 
enough  to  produce  solidification  at  all  temperatures  at- 
tained. 

It  appears  probable  that  the  earth's  internal  tempera- 

*  The  use  of  all  the  data  give* 

#=.676  ±  .076,  j/=.029  ±  .065, 

where  the  approximation  to  complete  rigidity  is  expressed  by  the  approximation 
of  the  value  of  x  to  unity ;  and  the  value  of  y  approaches  zero  as  the  amount  of 
fluid  friction  diminishes.  The  numbers  given  with  alternative  signs  are  the 
probable  errors.  The  use  of  only  the  Indian  data  gives 

a:=.931  ±  .056,  y=.l55  ±  .068. 


THE  EARTH.  345 

ture  does  not  continue  to  increase  downward  in  uniform 
ratio  with  the  depth,  but  that  the  rate  of  increase  dimin- 
ishes. As  to  the  internal  pressure,  it  must  increase  at  a 
rate  greater  than  the  increase  of  depth;  since  it  is  demon- 
strated that  the  density  of  terrestrial  matter  increases 
toward  the  centre.  The  mean  density  of  rocks  at  the 
surface  is  about  2.65,  while  the  mean  density  of  the  whole 
earth  is  about  5.5.  The  density  of  the  centre  is  made 
10.74  by  Pratt,  who  takes  surface  density  at  2.75;  and 
9.59,  by  Waltershausen,  who  takes  surface  density  at 
2.66.  The  law  of  increase  of  density  is  unknown,  but 
Waltershausen  has  assumed  a  formula*  which  gives  the 
density  inversely  as  the  square  of  the  distance  from  the 
centre;  and  Archdeacon  Pratt  has  adopted  and  independ- 
ently established  the  formula  of  Laplace,  which  makes 
the  increase  of  the  density  vary  as  the  square  root  of  the 
increase  of  pressure.  Each  successive  layer  of  uniform 
thickness  must  add,  therefore,  an  increasingly  greater 
amount  to  the  pressure  exerted  upon  the  parts  within, 
and  also  to  their  density,  unless  we  assume  that  the  com- 
pressibility of  terrestrial  matter  exists  only  within  certain 
limits  of  pressure. 

(2.)  In  the  next  place  we  may  suppose  that  at  all 
depths  beneath  the  surface  the  pressure  is  such  that  the 
fusing  point  is  higher  than  the  actual  temperature,  so  that 
a  state  of  solidity  exists.  If,  now,  the  pressure  within 
any  region  becomes  diminished  to  a.  certain  extent,  the 
fusing  point  may  be  lowered  to  the  actual  temperature, 
where  a  state  of  fusion  will  supervene.  Now,  we  may 
conceive  the  pressure  to  be  diminished  by  the  opening  of 
a  fissure  from  the  surface.  In  this  case,  all  the  matter 
relieved  may  dissolve  into  a  state  of  fusion,  and  this  first 

*  Waltershausen:  Rocks  of  Sicily  and  Iceland,  p.  315.    His  formula  is 

rr=P-CP-p)t* 

where  p'  is  the  density  at  the  distance  r  from  the  centre,  p  is  the  surface  density 
and  P  the  density  at  the  centre. 


346  SPECIAL  PLANETOLOGY. 

fused  matter  may  be  crowded  upward  through  the  fissure 
by  the  pressure  of  contiguous  matter,  which,  in  turn,  as 
soon  as  relieved,  will  be  fused  and  ejected  through  the 
fissure  in  a  similar  way.  Thus,  it  may  be  conceived,  a 
copious  fissure  outflow  of  melted  matter  might  be  occa- 
sioned. Or,  we  may  conceive  the  relief  from  pressure  to 
result,  as  Professor  William  Hopkins  suggested,  by  the 
partial  support  of  an  overlying  arch  bulged  up  by  lateral 
pressure.  Or,  finally,  we  may  look  to  the  removal  of  vast 
overlying  formations  by  surface  erosion,  as  the  source  of 
such  diminution  of  deep  pressure  as  would  lower  the 
fusing  temperature  to  the  actual  temperature.  Mr.  Clar- 
ence King  has  considered  this  cause  attentively,  and  has 
enunciated  the  opinion  that  it  answers  the  requirements 
of  the  case.*  He  has  remarked  that  periods  of  copious 
volcanic  overflow  have  followed  periods  of  extensive  ero- 
sion of  mountains  arid  plateaus,  and  that  the  succession  in 
the  nature  of  the  erupted  materials  at  different  localities 
and  different  epochs  is  such  as  is  best  explained  by  the 
supposition  of  isolated  lakes  of  molten  matter,  such  as 
would  arise  from  local  and  somewhat  sudden  diminution 
of  pressure,  f 

(3.)  We  may  conceive  that  heat  and  fusion  result  from 
some  mechanical  crushing  pressure.  With  Mallet  and 
others  we  may  conclude  that  local  fusion  is  produced 
through  the  crushing  effects  of  enormous  lateral  pressure 
resulting  from  the  secular  contraction  of  the  earth  in  its 
slow  process  of  cooling.  Mr.  Mallet  advocated  this  view 

*  King:  Geolog.  Exploration  Wh  Parallel,  i,  p.  706,  seq. 

t  In  the  foregoing  paragraph  I  have  employed  the  usual  language,  but,  as 
before  explained  (p.  270),  I  do  not.  consider  it  exact,  since  the  solidification  which 
exists  at  great  depths  and  at  a  high  temperature,  is  not  analogous  with  normal 
crystalline  freezing,  but  is  merely  a  consolidation  by  confinement  of  molecules 
in  fixed  positions.  Pressure  lowers  the  normal  freezing  point  of  molten  rocks 
instead  of  raising  it.  But  the  principle  stated  is  valid  under  either  view. 


THE  EARTH.  347 

with  great  ability  and  great  persistence.*  But  it  has  been 
opposed  as  inadequate  by  numerous  competent  writers,  j- 
By  some  it  has  been  shown  that  the  total  contraction  of 
the  earth  is  insufficient,  and  by  others,  that  the  effects  are 
so  much  diffused  as  not  to  attain  a  condition  of  disturb- 
ance at  distinct  localities.  It  may  fairly  be  claimed,  never- 
theless, that  the  effects  of  contraction  would  be  diffused 
only  in  proportion  as  all  the  physical  conditions  of  the 
earth's  crust  are  everywhere  uniform;  while  such  uniform- 
ity is  contradicted  by  all  our  familiar  observations  on  the 
crust.  So  far  as  secular  contraction  gives  rise,  therefore, 
to  lateral  pressure,  we  must  expect  the  crushing,  and 
therefore  the  heating  effects,  to  be  accumulated  in  the 
weakest  regions  of  the  crust. 

But  a  cause  of  crushing  pressure  which  seems  to  me 
more  adequate  than  secular  cooling  is  suggested  by  Sir 
William  Thomson's  and  Archdeacon  Pratt's  and,  we  may 
add,  Professor  G.  H.  Darwin's,  demonstrations  of  tidal 
effects  in  a  globe  as  rigid  as  steel  or  glass.  May  not 
the  tidal  deformations  of  the  earth's  crust  be  the  source 
of  the  internal  heat  which  manifests  itself  in  fluidity?  The 
whole  value  of  the  lunar  tidal  oscillation  in  a  yielding 
globe  should  be  about  58  inches.  In  a  globe  as  rigid  as 
glass  it  should  therefore  be  about  34.8  inches,  and  in  one 
as  rigid  as  steel,  19.33  inches.  The  whole  tidal  oscillation 
under  the  joint  maximum  influence  of  the  sun  and  moon 
in  a  perfectly  yielding  globe  would  be  about  81.2  inches. 

*  Besides  a  long  series  of  memoirs  on  the  theory  and  phenomena  of  volca- 
noes and  earthquakes,  cited  in  the  author's  Syllabus,  p.  73,  the  reader  may  con- 
sult, especially,  Mallet,  On  the  Temperature  Attainable  by  Rock-crushing,  and 
its  Consequences,  Phil.  Mag.,  July  1875, 1-13.  and  Amer.  Jour.  Sci.,  Ill,  x,  256-68, 
and  xii,  463;  also  Phil.  Mag.,  v,  i,  19-22. 

tSir  W.  Thomson,  Nature,  Jan.  18  and  Feb.  1,  1872;  O.  Fisher,  Quar.  Jour. 
Gtol.  Soc.,  Lond.,  xxxi,  469-72,  May  12.  1875;  Phil.  Mag.,  iv,  1,  302-19,  Oct.,  1875; 
id.,  v,  i.  38-42;  Physics  of  the  EaiWs  Crust,  ch.  iv,  v,  vi.  Criticisms  are  made 
also  by  Gen.  G.  J.  Barnard,  Smithsonian  Contributions,  No.  240,  and  by  E.  W. 
Hilgard,  Amer.  Jour.  Sci.,  Ill,  vii,  535-46,  June,  1874,  and  I'hil.  Mag.,  July,  1874, 
41. 


348  SPECIAL    PLANETOLOGY. 

The  amount  in  a  globe  of  glass  would  therefore  be,  when 
at  a  maximum,  48.72  inches  and  in  a  globe  of  steel,  27. OG 
inches.  Should  the  terrestrial  globe  yield  to  the  extent 
of  any  one  of  these  amounts,  the  crushing  effect  expe- 
rienced by  the  superior  zones  of  the  crust  would  not  be 
uniformly  distributed,  since  variations  in  structure  and 
hardness  and  surface  configuration  would  preserve  certain 
portions  from  any  change,  and  the  whole  amount  of  the 
interstitial  displacements  would  be  accumulated  in  the 
remaining  portions.  It  does  not  seem  at  all  improbable 
that  the  transformation  of  such  enormous  mechanical  force 
into  heat  should  suffice  to  bring  to  a  state  of  fusion  vol- 
umes considerable  enough  to  answer  all  the  requirements 
of  the  thermal  manifestations  of  modern  times,  as  well  as 
the  terrestrial  movements  of  modern  earthquakes. 

The  extended  series  of  observations  on  earthquake  phe- 
nomena collected  by  the  late  M.  Alexis  Perrey  and  by  the 
British  Association,  are  generally  thought  to  indicate  a 
real  connection  between  such  phenomena  and  the  positions 
of  the  sun  and  moon.  Thus  (a)  earthquake  shocks  are 
more  frequent  at  the  time  of  lunar  syzygies  than  at  the 
quadratures.*  As  the  tidal  effects  of  the  moon  and  sun 
are  as  5  to  2,  their  conspiring  effects  at  the  syzygies  are 
as  7  and  their  conflicting  effects  at  quadratures  are  as  3. 
If  the  seismic  consequences  of  a  range  from  7  to  3  are 
observable  as  a  differential  —  that  is,  if  a  tidal  influence 
represented  by  4  is  a  reality,  then  still  more  must  a  tidal 
influence  represented  by  5  or  ?  be  a  reality. 

(£»)  Seismic  phenomena  are  more  frequent  when  the 
moon  is  in  perigee  than  when  in  apogee.f  The  difference 
between  the  maximum  and  minimum  distances  of  the 
moon  from  the  earth  is  about  31,355  miles.  The  tide-pro- 

»  A.  Perrey,  cited  in  Amer.  Jour.  8d.,  II,  xxxvii,  1;  III,  xi,  233;  Pop.  Sci. 
Monthly,  xvii,  457. 

+Pop.  Sci.  Monthly,  xvii,  458. 


THE   EARTH.  349 

ducing  efficiency  of  an  attracting  body  is  inversely  as  the 
cube  of  the  distance.  The  lunar  tide  in  perigee  will  there- 
fore be  to  the  lunar  tide  in  apogee  as  1.487  to  unity. 
Here  is  a  variation  amounting  to  49  per  cent  of  the  apogee 
tidal  efficiency.  A  variation  of  49  per  cent  of  the  mini- 
mum tide-producing  efficiency  is,  it  thus  appears,  the 
cause  of  a  certain  observed  variation  in  earthquake  action. 
The  whole  lunar  force,  therefore,  may  be  the  cause  of 
the  regular  body  of  seismic  phenomena. 

(c)  Earthquakes  are  more  frequent  with  the  moon  in 
the  meridian  than  with  the  moon  in  the  horizon.  In  the 
former  case,  the  lunar  tide  is  at  flood  or  nearly  so,  and  in 
the  latter,  nearly  at  ebb.  This  result  confirms  the  conclu- 
sion that  lunar  attractions  cause  relative  movements  in 
different  parts  of  the  terrestrial  crust,  and  show  that  the 
elevatory  effects  are  more  disturbing  than  the  ebb-tide 
subsidences.  When  the  crust  over  two  opposite  quarters 
of  the  earth's  surface  subsides  simultaneously  with  corre- 
sponding elevations  over  the  two  intervening  quarters,  it 
perhaps  results  that  the  subsiding  quadrants  are  more  uni- 
formly and  more  firmly  braced  than  the  rising  quadrants, 
and  would  therefore  experience  less  local  motion  than 
they. 

The  observational  determination  and  measurement  of 
the  geological  tide-wave  is  a  subject  of  extreme  delicacy. 
Were  all  the  disturbing  influences  acting  on  the  oceanic 
waves  suspended  for  a  period,  observation  would  readily 
determine  the  actual  fluctuation  caused  by  lunar  and  solar 
attractions,  and  the  difference  between  these  and  the  fluc- 
tuations deducible  on  the  theory  of  a  perfectly  rigid  globe 
would  reveal  the  extent  which  the  earth  falls  short  of  per- 
fect rigidity.  It  is  probable  that  tidal  observations,  made 
under  the  direction  of  the  highest  science,  will  ultimately 
eliminate  disturbing  effects  arising  from  winds,  barometric 
oressure  and  other  causes,  and  make  known  the  actual  ex- 


350  SPECIAL   PLANETOLOGY. 

tent  of  tidal  fluctuations  in  the  open  sea.  Sir  William 
Thomson  has  pointed  out  some  conceivable  experiments 
which  would  result  in  the  very  desirable  solution  of  this 
problem.  He  supposes  a  water  pipe  twelve  kilometers  in 
length,  submerged  to  protect  it  from  variations  in  atmos- 
pheric pressure,  and  turned  up' at  each  end  into  the  free 
atmosphere.  Then,  if  the  earth  were  perfectly  rigid,  and 
the  pressure  of  the  air  equal  at  the  two  extremities,  the 
water  would  rise  in  the  more  southern  end  during  the  pas- 
sage of  the  moon  over  the  meridian.  Or,  if  a  plumb  line 
were  suspended  from  a  great  height,  and  could  be  kept 
perfectly  free  from  atmospheric  disturbance,  it  would  be 
deflected  always  toward  the  nearest  tidal  swell,  except 
that  when  the  moon  were  in  the  horizon  or  in  the  meridian, 
the  attractions  from  opposite  directions  would  neutralize 
each  other.  The  greatest  deflection  would  always  be  at 
the  distance  of  45°  north  or  south  of  the  position  corre- 
sponding to  the  moon's  declination,  and  the  greatest  deflec- 
tion for  any  particular  locality  would  be  when  the  moon  is 
45°  above  or  below  the  horizon.  The  greatest  deflection 
of  the  line,  however,  would  be  only  one  twelve-millionth 
of  its  length,  and  this  movement  could  hardly  be  made 
perceptible  in  a  line  of  any  practicable  length. 

2.  Submeridional  Trends  in  the  Earth's  Primitive 
Structure.  —  As  important  tidal  influences  must  always 
have  existed  on  the  earth's  surface,  we  may  continue  to 
discover  in  the  oldest  records  of  the  earth's  solidifying 
state,  some  traces  of  tidal  action.  I  am  inclined  to  think 
we  discover  such  in  the  prevailing  meridional  trends  of  the 
oldest  mountain  ranges.  I  have  stated  that  the  trans- 
meridional  progress  of  the  tidal  swell  in  early  incrustive 
times  on  any  planet,  must  give  the  forming  crust  structural 
characteristics  and  aptitudes  trending  from  north  to  south. 
I  have  stated  also  that  the  horizontal  component  of  the 
tidal  action  on  a  lagging  tidal  swell  would  tend  to  give 


THE   EAETH.  351 

the  swell  an  actual  motion  of  translation  toward  the  west. 
Suppose  the  tide-wave  to  lag  an  hour  behind  the  moon's 
meridian  passage,  it  can  readily  be  shown  that  the  horizon- 
tal component  of  the  moon's  attraction  upon  the  wave  is 
one  two  hundred  and  twenty-sixth  of  the  whole  tide-pro- 
ducing effort  of  the  moon.*  Such  a  motive  to  actual 
translatory  motion  is  by  no  means  inconsiderable  —  the 
less  so  when  we  reflect  that  it  is  not  directly  opposed  by 
gravity,  as  in  the  case  of  the  tidal  elevation,  but  only  by 
the  friction  and  inertia  of  the  water. 

When,  therefore,  the  earliest  wrinkles  came  into  exist- 
ence their  axes  would  be  meridional  or  submeridional. 
Now,  some  of  the  oldest  beginnings  of  mountain  devel- 
opment upon  the  earth  are  seen  in  the  submeridional 
Laurentian  ridges;  in  some  of  the  Appalachian  ranges,  as 
the  Blue  Ridge,  the  Highlands  of  New  York  and  Black 
Mountain  of  North  Carolina;  in  some  ranges  of  the  Rocky 
Mountains,  as  Colorado,  Medicine  Bow  and  Park  Ranges, 
in  the  Humboldt  Range,  and  in  the  whole  system  of  the 
so-called  "Basin  Ranges."  Not  materially  later  are  the 
Green  Mountains,  the  White  Mountain  system,  the  other 
principal  orographic  foundations  of  the  Rocky  Mountain, 
Sierra  Nevada  and  Cascade  chains,  all  equally  meridional. 
In  Europe,  the  Scandinavian  range,  the  Urals,  the  Cam- 
brian Mountains,  the  East  Adriatic  Alps;  in  Asia,  the 
Yablonoi,  the  ranges  of  Indo  China,  the  Malayan  penin- 
sula and  islands,  and  those  of  Japan,  Kamtchatka  and 
northeastern  China;  in  Africa,  the  entire  east  and  west 
coast  ranges,  and  those  of  Madagascar,  all  conform  approx- 
imately to  the  direction  of  the  meridian.  It  is  also  proba- 

*  If  in  the  formula  previously  given  (p.  233)  we  assume  in  the  case  of  the 
moon  and  earth,  a=15°,  TO=3959andE  T=240,000,  then  T  A=Fx*f?HHhrX  tan 
15°  =  .00442F=sTjff  F  nearly,  where  F  represents  the  moon's  attraction  at  the 
earth's  surface  and  T  A  represents  roughly  its  horizontal  component  at  the  dis- 
tance of  15°  from  the  zenith  point. 


352  SPECIAL   PLANETOLOGY. 

ble  that  the  foundations  were  early  laid  for  the  Sierra 
Madre  Mountains  in  Mexico,  and  the  Andes  and  the  Serro 
Espinaco  and  Organ  Mountains  of  South  America.  The 
crests  of  these  mountain  ranges  may  probably  be  regarded 
as  ancient  co-tidal  lines,  and  these  mountains  are,  to  some 
extent,  frozen  billows,  in  the  solidifying  terrestrial  surface, 
thrust,  indeed,  far  above  their  original  altitudes  by  the 
lateral  pressure  to  which  the  shrinkage  of  the  earth's 
interior  has  subjected  them. 

More  than  this,  the  whole  general  expression  of  the 
earth's  surface  configuration  should  preserve  traces  of  the 
same  primitive  tidal  action.  (1)  The  original  continental 
masses  should  trend  generally  with  the  meridian.  This  is 
the  fact  with  North  America,  South  America,  Greenland 
and  Africa.  Moreover,  an  ancient  Scandinavian  continent 
stretched  from  Spitzbergen  to  the  Straits  of  Dover,  while 
most  of  other  parts  of  Europe  were  sea  bottom.  The 
ancient,  but  now  much  wasted  continent  which  embraced 
Australia,  New  Guinea,  Borneo  and  the  Philippine  Islands, 
had  a  submeridional  trend.  The  Mascarene  continent, 
including  Madagascar,  stretched  north  and  south.  The 
group  of  New  Zealand  islands,  with  the  contiguous  sub- 
marine mass,  is  elongated  meridionally.  (2)  The  great 
ocean  basins  and  their  submarine  topography  should 
reveal  a  similar  influence.  Accordingly  the  Atlantic  and 
Pacific  have  their  longer  axes  north  and  south,  arid  the 
submarine  topography  of  the  Atlantic,  so  far  as  known, 
generally  corresponds.  As  to  the  configuration  of  the 
Pacific  Ocean,  Prof.  J.  D.  Dana  pronounces  it  "remark- 
able," and  calls  attention  to  the  fact  that  "nearly  all  the 
ranges  of  islands  over  the  Pacific  Ocean,  and  even  the 
longer  diameters  of  the  particular  islands,  lie  nearly  paral- 
lel with  the  great  mountain  ranges  of  the  Pacific  coast  of 
North  America."  This  arrangement  he  refers  to  the 
structure  of  the  infra- Archaean  crust.  The  method  of  sub- 


THE   EARTH.  353 

sidence  of  the  coral  islands  over  a  breadth  of  more  than  a 
quarter  of  the  earth's  circumference  develops  similar  and 
parallel  trends.*  (3)  Many  accessory  features  of  land 
and  water  might  be  expected  to  retain  traces  of  early 
geognostic  conformations  now  partially  obliterated.  I 
think  we  may  discover  these  in  the  basin  of  Hudson's  Bay 
and  the  seas  and  sounds  stretching  thence  northward  to 
the  Arctic  Ocean;  in  Baffin's  Land  and  Baffin's  Bay;  in 
the  valleys  of  the  St.  Lawrence,  Mackenzie  and  Mississippi 
Rivers,  and  the  Nile,  Volga,  Ural,  Obi,  Yenesei,  Lena, 
Indus,  Ganges,  Brahmaputra  and  others;  in  the  general 
trend  of  the  West  Indian  Islands;  in  the  form  of  Great 
Britain  and  the  contiguous  islands,  in  the  Baltic,  the  Red 
and  Caspian  Seas  ;  in  Novaya  Zemlia  and  the  Gulf  of 
Obi;  in  Kamtchatka,  the  Sea  of  Okhotsk,  the  Japan  Sea, 
the  Yellow  Sea ;  in  the  great  alternating  bays  and  penin- 
sulas of  the  south  of  Asia;  and  finally,  in  the  north  and 
south  trends  of  minor  features  which  have  been  deter- 
mined immediately  by  the  strike  of  geological  formations, 
such  as  the  Adriatic,  the  ^Egean  and  the  Italian  peninsula, 
Lakes  Tanganyika  and  Albert  Nyanza  in  Africa,  and  in 
Lakes  Michigan  and  Huron  and  in  Saginaw,  Georgian, 
Thunder,  Green  and  Grand  Traverse  Bays  pertaining  to 
these  lakes  in  North  America. 

But  there  are  many  terrestrial  features  which  do  not 
conform  to  the  requirements  of  this  theory.  In  reference 
to  these  there  are  two  observations  to  be  made :  (1)  When  we 
regard  the  general  expression  conveyed  by  the  aggregate 
of  the  earth's  surface  features,  we  find  that  the  general 
meridional  impress  is  unmistakable.  (2)  The  meridional 
features  are  generally  connected  with  the  most  primitive 
geognostic  condition,  and  the  transmeridional  features  can 
generally  be  shown  to  be  of  later  origin,  and  to  owe  their 
existence  to  agencies  which  came  into  being  only  in  the 
*Dana,  4mer.  Jour.  Sci.,  Ill,  v,  442-3, 


354  SPECIAL   PLANETOLOGY. 

later  progress  of  the  world's  development.  The  most  im- 
portant of  these  are:  First,  the  transverse  stretch  of  the 
continent  of  Eurasia.  Now,  when  we  look  at  a  map  of 
this  continent  we  see  that  it  is  distinctly  impressed  by 
profound  meridional  characteristics.  The  numerous  great 
rivers  flowing  northward  along  their  several  valleys  almost 
interlock  with  the  great  bays  projecting  northward  from 
the  Indian  Ocean.  The  general  land  area  is  clearly 
marked  by  a  series  of  meridional  rugosities,  and  the  fact 
that  the  intervening  depressions  are  now  permanently 
above  the  sea  level  is  an  unimportant  circumstanse.  Were 
this  continent  to  undergo  a  subsidence,  the  waters  of  the 
Arctic  and  Indian  Oceans  would  meet  at  several  points.  In 
confirmation  of  these  views  we  learn  that  the  oldest  known 
rocks  of  China  —  the  old  Archaean  gneisses  —  maintain  a 
pretty  uniform  strike  from  north-northwest  to  south- 
southeast.*  Further,  it  cannot  be  doubted  that  the  lateral 
pressure  of  oceans  has  contributed  greatly  to  the  develop- 
ment of  folds  along  lines  parallel  with  the  ocean  shores. 
This  is  an  important  part  of  the  immediate  agency  which 
has  uplifted  so  many  coastwise  mountain  ranges.  The 
ocean  shore  is  indeed  generally  a  feature  which  has  been 
alreadv  determined  by  the  movement  of  the  primitive 
tidal  swell;  but  if  an  ocean  shore  from  any  cause  stretches 
across  the  meridians,  contrary  to  the  influence  of  the  tidal 
swell,  there  must  exist  a  strong  motive  for  the  development 
of  transverse  mountain  ridges.  Now  such  a  relation  exists 
between  the  mountains  of  central  Asia  and  the  Indian 
Ocean;  and  between  the  Pyrenees,  Alps,  Carpathians  and 
Caucasus,  and  the  Mediterranean  Sea  —  once  much  longer, 
broader  and  deeper  than  at  present.  Secondly,  the  moun- 
tains of  central  Europe  and  the  Mediterranean  Sea.  The 
sea  undoubtedly  sustains  some  causal  relation  to  these 
mountains,  as  well  as  the  Atlas  chain  in  north  Africa. 
*VonRichthofcn:  China,  vol.  ii. 


THE   EARTH.  355 

But  in  its  insular  and  littoral  features  we  can  even  trace 
some  relation  to  a  deep-seated  meridional  structure.  This 
is  exemplified  in  the  chain  of  Corsica  and  Sardinia;  in  the 
Italian  peninsula  and  the  Adriatic;  in  the  ./Egean;  in  the 
Syrtes  Major  and  Minor,  and  in  the  truncated  eastern  ex- 
tremity. How  the  Mediterranean  and  Indian  Ocean  shores 
came  to  have  general  transmeridional  trends  is  a  question 
which  must  find  its  solution  in  the  events  of  Mesozoic  and 
Cnenozoic  geological  history.  It  suffices  to  observe  that 
the  action  which  determined  these  shore  lines  belongs  to 
medial  and  later  geologic  times,  when  the  geotidal  influ- 
ences had  ceased  to  be  active,  and  exerted  themselves  only 
in  the  form  of  a  store  of  meridional  predispositions  which 
the  powerful  strains  borne  by  a  greatly  thickened  crust 
might  well  be  supposed  adequate  to  overcome.  Thirdly,  the 
valley  of  the  Amazons  is  a  great  transmeridional  feature. 
It  occupies,  however,  like  the  Amur,  a  great  post-paleo- 
zoic basin.  This  stretched  southward  from  the  mouth  of 
the  Amazons  —  like  the  ancient  intra-Mediterranean  pro- 
longation of  the  Gulf  of  Mexico  stretching  northward  — 
and  really  constituted  a  primitive  meridional  feature,  such 
as  will  probably  be  revealed  in  the  geological  structure  of 
Asia.  This  southward  basin  seems  to  have  been  closed  up 
in  southern  Brazil  by  the  development  of  converging 
ranges  of  mountains  on  the  east  and  west  limbs  of  South 
America;  so  that  the  present  valley  of  the  Amazons  is 
merely  the  transverse  dimension  of  an  ancient  depression 
at  its  widest  part. 

3.  The  Earths  Age,  with  Methods  of  Calculation. — 
As  to  the  numerical  expression  of  the  age  of  the  world, 
various  guesses  and  calculated  results  have  been  given  on  a 
previous  page  (p.  179).  The  grounds  of  various  estimates 
of  the  age  of  the  world  or  of  certain  periods  may  be  enu- 
merated as  follows: 

(1.)  The  time  required  for  the  sun  to  contract  from  a 


356  SPECIAL   PLANETOLOGY. 

nebulous  condition,  or  from  the  orbit  of  the  earth  to  its 
present  limits.  Professor  Newcomb  says  the  heat  evolved 
by  contraction  from  an  infinite  distance  would  last  only 
18,000,000  years.*  A  temperature  permitting  the  exist- 
ence of  water  on  the  earth  would  have  been  reached  10,- 
000,000  years  ago. 

(2.)  The  time  which  the  sun  will  require  to  cool  from 
its  present  condition  to  a  darkened  or  planetary  state. 
Newcomb  says  the  sun  at  its  present  rate  of  radiation  will 
be  as  dense  as  the  earth  in  12,000,000  years;  and  it  is 
quite  likely  to  be  long  before  that  time  that  we  are  to  ex- 
pect the  permanent  formation  of  a  continuous  crust.f 

(3.)  The  time  required  for  the  earth  to  cool  from  incipi- 
ent incrustation  to  its  present  state,  based  on  the  thermal 
conductivity  of  rock-masses  and  the  rate  of  increase  of 
heat  toward  the  earth's  centre.  Sir  William  Thomson  con- 
cludes that  this  time  cannot  exceed  80,000,000  years,  t 
Rev.  O.  Fisher,  on  a  similar  basis,  calculates  that  the 
incrusted  age  of  the  world  cannot  exceed  33,000,000  years. 
M.  Elie  De  Beaumont  calculated  that  38,359  years  must 
have  passed  after  the  beginning  of  incrustation,  before  the 
rate  of  cooling  in  the  general  interior  would  surpass  that 
of  the  crust.  At  this  epoch  the  formation  of  mountains 
would  begin.§ 

(4.)  Relative  times  required  for  the  deposition  of  all 
the  rocky  sediments.  This  method  by  itself  furnishes  no 
clew  to  absolute  times,  but  only  to  time  ratios.  It  makes 
the  thickness  of  a  bed  of  sediments  the  measure  of  the 
time  consumed  in  its  deposition.  Undoubtedly,  each  bed 
is  thus  measured;  but  it  cannot  be  assumed  that  a  con- 
stant relation  exists  between  time  and  thickness  of  sedi- 

*  Newcomb:  Popular  Astronomy,  509. 
t  Newcomb:  Popular  Astronomy,  513. 

JThomson  and  Tait:  Nat.  Phil.,  1st  ed.  Conip.  Croll:  Climate  and  Time, 
335.  Fisher :  Physics  of  the  Earth's  Crust,  71. 

eaumont:  1^8  Systintes  de  Montagnes, 


THE   EARTH.  357 

ments.  At  some  epochs,  and  probably  during  whole 
periods  and  ages,  the  energy  of  the  forces  of  deposition 
must  have  been  more  rapid  than  at  other  epochs  and 
during  other  intervals  of  time.  During  the  same  interval 
the  rate  of  deposition  must  be  more  rapid  in  one  region 
than  in  another.  This  difference  must  arise  from  differ- 
ences in  the  activity  of  the  same  class  of  forces,  and  from 
differences  in  the  kind  of  agency  employed.  Fragmental 
sediments  accumulate  more  rapidly  than  calcareous;  and 
the  ratio  of  the  two  which  is  generally  adopted  regards 
one  foot  of  limestones  equivalent  to  five  feet  of  sandstones 
or  shales. 

Notwithstanding  unavoidable  inaccuracies,  the  method 
furnishes  results  of  considerable  value  and  interest.  If 
the  maximum  thicknesses  of  the  formations  are  taken  from 
the  Same  geogiiostic  region,  as  for  instance  the  region  of 
Appalachian  upbuilding,  the  ratio  of  the  thicknesses  may 
be  nearly  the  same  as  in  another  region  where  the  rate  of 
accumulation  is  less.  By  taking  the  limestones  from  the 
same  region  we  avoid  exaggerating  estimates  for  the  same 
periods.  The  geognostic  region  of  most  active  accumula- 
tion during  Eozoic  time  was  the  Laurentian;  that  during 
Palaeozoic  time  was  the  Appalachian,  and  that  during 
Mesozoic  and  Caenozoic  time  was  the  Rocky  Mountain 
region  and  that  of  the  Great  Plains.  Within  each  region 
we  may  assume  the  progress  of  sedimentation  uniform. 
We  do  not  know  that  the  progress  in  one  region  during 
one  time  is  comparable  with  the  progress  in  another 
region  during  another  time;  but,  so  far  as  concerns  shore 
action,  we  are  compelled  to  assume  it  to  be  so.  For 
instance,  we  must  assume  that  ten  thousand  feet  of  Ter- 
tiary sediments  accumulated  by  shore  action  in  the  Rocky 
Mountains  correspond  to  the  same  length  of  time  as  ten 
thousand  feet  of  the  same  kind  of  sediments,  accumulated 
in  the  Appalachian  region  during  Pakeozoic  time.  We 


358  SPECIAL   PLANETOLOGY. 

can  understand,  however,  that  the  total  sedimentation  in  a 
given  length  of  time  must  have  been  greater  in  the  later 
periods,  when  the  land  areas  were  more  extensive,  and 
river  drainage  brought  larger  contributions  to  the  sea-bot- 
tom deposits.  What  allowance  should  be  made  for  river 
action  in  the  later  ages  it  is  impossible  to  state  with  any 
precision;  but  it  will  not  probably  exceed  the  require- 
ments to  allow  one-half  from  the  f ragmen tal  deposits  in 
the  Tertiary  lakes  and  seas  of  the  Rocky  Mountain  region, 
and  one-fifth  from  the  fragmental  deposits  of  the  Mesozoic 
ages  of  the  same  region. 

This  general  method  of  determining  time  ratios  has 
been  employed  by  Professor  James  D.  Dana,*  who  gives 
the  following  table  for  maximum  thicknesses. alpnjr  the 


Appalachians: 


Knitriiifrital  Limqjfcones. 

Roi" 


iocks. 

1.  Potsdam   Period 7.000  200 

2.  Rest  of  Lower  Silurian  18,000  6.000 

3.  Lower  Silurian  Era 25,000  6,200 

4.  Upper  Silurian  Era 6,760  600 

5.  Devonian  Age 14,300  100 

6.  Carboniferous  Age 16,000  125 


Totals,  feet 87,060  13,225 

Supposing  limestones  accumulate  at  one-fifth  the  rate 
of  fragmental  sediments,  the  above  numbers  become 
respectively  (1)  8,000;  (2)  48,000;  (3)  56,000;  (4)  9,760; 
(5)  14,800;  (6)  16,625.  These  numbers  have  nearly  the 
ratio  of  1  :  6  :  7  :  1±  :  2  :  2.  "  Hence,  for  the  Silurian, 
Devonian  and  Carboniferous  ages,  the  relative  duration 
will  be  8£  :  2  :  2,  or  not  far  from  4:1:1.  Or,  the  Silu- 
rian Age  was  four  times  as  long  as  either  the  Devonian 
or  Carboniferous;  and  the  Lower  Silurian  Era  nearly  six 
times  as  long  as  the  Upper  Silurian." 

For  the  Mesozoic,  Professor  Dana  announces  the  time 
ratios  as,  Triassic  1  :  Jurassic  1^  ;  Cretaceous  1.  For  the 

*Dana:  Manual  of  Geology,  Sded.,  381,  481,  585. 


TEE    EAETH.  359 

Cienozoic  he  finds  the  maximum  thickness  of  the  Tertiary 
deposits  16,000  feet,  with  very  little  limestone.  But  as 
river  action  increased  with  enlargement  of  the  land  areas, 
he  reduces  this  thickness  one-half  to  arrive  at  the  approxi- 
mate amount  of  marine  sedimentation.  Then,  assuming 
the  Quaternary  to  have  been  one-third  as  long  as  the 
Tertiary,  he  gets  the  ratios,  Palaeozoic  12  :  Mesozoic  3 
:  Caenozoic  1. 

The  following  table  of  the  approximate  thickness  of 
the  several  geological  formations  in  Europe  —  making  no 
discriminations  for  limestones  or  for  fluvial  contributions 
—  has  been  compiled  by  Rev.  S.  Haughton,  of  the  Uni- 

versity of  Dublin:* 

Feet. 
1.     Eozoic  ..............................................  26,000 


2      T  nwpr  Pala-ozoio     J  Lower  Silurian 

2.  Lower  Palaeozoic.  ^  Upper  Silurian  ...................     5,500 

(  Devonian  ........................     9,150 

3.  Upper  Palaeozoic  .   -  Carboniferous  ...................   14,600 

(Permian  ...........  .............  3,000 

f  Triassic  ..........................  2,200 

Jurassic  .........................  4,590 

4.  Neozoic  .........  4  Cretaceous  .......................  11,283 

Nummulitic  [Middle  Eocene]  ......     3,000 

[Tertiary  ........................  .     6,000 

110,323 

From  this,  by  disregarding  Quaternary  and  including 
the  Nummulitic  in  the  Csenozoic,  we  get  the  ratios,  Eozoic 
4.7  :  Lower  Silurian  4.5  :  Upper  Silurian  1  :  Upper  Pa- 
laeozoic 4.9  :  Mesozoic  3.3  :  Casnozoic  1.6. 

In  attempting  to  compile  results  from  the  latest  deter- 
minations of  thickness  in  the  several  formations,  nothing 
better  can  be  done  than  to  accept  for  the  Eozoic  Great 
System,  the  conclusions  of  Sir  William  Logan  for  the 
Laurentian  region.  These  give  us  for  the  maximum 
thickness  of  the  Laurentian  30,000  feet,  of  which  lime- 
stone masses  aggregate  3,500  feet,  or,  deducting  inter- 
calated beds  of  gneiss,  2,800  feet.  For  the  Huronian, 

t  Haughton,  Phil.  Mag.,  xxvi,  545,  Dec.  20,  1877. 


360  SPECIAL   PLANETOLOGY. 

Logan's  estimate  was  a  maximum  of  20,000  feet,  with 
only  thin  layers  of  somewhat  impure  limestone,  which 
we  may  set  down  at  100  feet. 

Turning  to  the  Palaeozoic  ages  and  the  Appalachian 
region,  in  its  extension  to  Nova  Scotia,  we  may  deduce 
the  following  statement  of  maximum  thicknesses: 

PRIMORDIAL  GROUP. — Acadian  attains  10,000  feet  in 
the  Ocoee  slates  and  conglomerates  of  east  Tennessee. 
Potsdam,  5,600  feet  of  limestones,  sandstones  and  shales 
in  Newfoundland,  of  which  200  feet  may  be  set  down  as 
limestones.  Total  fragmental,  15,408;  limestone',  200. 

CANADIAN  GROUP. —  Calciferous  attains  7,000  feet  in 
east  Tennessee,  of  which  3,000  feet  are  fragmental  and 
4,000  feet  chiefly  limestones.  Quebec,  6,600  feet  in  New- 
foundland, including  3,200  feet  of  limestone.  Chazy, 
600  feet  in  east  Tennessee,  principally  limestone.  Total 
fragmental,  6,400  feet;  limestone,  7,800. 

TRENTON  GROUP. —  Trenton,  in  east  Tennessee,  2,000 
feet  of  limestones  and  shales,  of  which  500  feet  may  be 
assumed  as  shales.  Utica,  700  feet  of  shales  in  Pennsyl- 
vania. Hudson  River,  1,259  feet  of  limestone  at  Anti- 
costi,  or  2,000  feet  of  shales  near  Quebec,  or  6,000  feet  of 
shales  in  Pennsylvania.*  Total  fragmental,  7,200  feet; 
limestones,  1,500  feet. 

NIAGARA  GROUP. — Medina,  attains  2,500  feet  of  con- 
glomerates and  sandstones  in  Pennsylvania.  Clinton, 
2,555  feet  of  shales  in  Pennsylvania.  Niagara,  in  Pennsyl- 
vania embraces  450  feet  of  marl  or  fragile  shale,  and  1,200 
feet  of  the  same  with  thin  limestone  layers.  Consists 
of  350  feet  of  limestone  in  Iowa,  which  is  nearly  equiv- 
alent. Total  fragmental,  6,605  feet;  limestones,  100  feet. 

SALINA  GROUP  presents  a  maximum  of  1,650  feet  in 
Pennsylvania,  of  which  not  over  100  feet  can  be  set  down 
as  limestones. 

*  Lesley :  2d  Penn.  Survey,  G  6,  p.  152. 


THE   EARTH.  361 

LOWER  HELDERBERG  GROUP  presents  a  maximum  at 
Cape  Gaspe  of  about  1,500  feet  of  limestones. 

ORISKANY  GROUP  attains  520  feet  of  calcareous  shales 
and  argillaceous  sandstones  in  Pennsylvania,  of  which  not 
over  50  feet  could  be  counted  as  limestone. 

CORNIFEROUS  GROUP. —  Caucla  Galli  Grit  attains  300 
feet  in  eastern  Pennsylvania,  and  Corniferous  limestone 
500  feet  in  northwestern  New  Jersey. 

HAMILTON  GROUP. — The  Gasp6  sandstones  present  a 
maximum  of  6,000  feet.  Otherwise  we  might  take  the 
Marcellus  shale,  with  some  argillaceous  limestone,  in 
Pennsylvania,  at  1,300  feet  (I.  C.  White) — not  over  50 
feet  limestones  —  the  Hamilton  proper  in  Pennsylvania,  at 
1,375  feet  (I.  C.  White)  of  shales  and  sandstones,  and  the 
Genesee,  also  in  Pennsvlvania,  at  700  feet  of  black  calca- 
reous shale  (not  over  50  feet  limestone),  making  fragmental 
3,275  feet,  and  limestone  100  feet.  But  we  shall  adopt  the 
Gaspe"  measure. 

CHEMUNG  GROUP. —  Portage  amounts  to  1,700  feet  of 
flaggy  sandstones  and  blue  shales  in  Pennsylvania.  Che- 
mung,  3,200  feet  of  sandstones,  shales  and  conglomerates 
along  the  Appalachians.  Total,  4,900  feet  fragmental. 

CATSKILL  GROUP  aggregates  6,000  feet  of  sandstones, 
shales  and  conglomerates  along  the  Appalachians,  reaching 
7,544  feet  in  Carbon  county,  Pennsylvania,  all  of  which  is 
fragmental  except  14  feet  of  calcareous  breccia. 

LOWER  CARBONIFEROUS  series  in  Pennsylvania  ag- 
gregates 5,560  feet  of  shales  and  sandstones  with  some 
(say  500  feet  of)  limestones.  On  the  eastern  border, 
6,000  feet  of  sandstones,  marls,  marlites  and  gypsum;  in 
Tennessee  and  Alabama,  2,170  feet  of  limestones,  which 
is  equivalent  to  10,850  feet  fragmental.  It  may  be  best 
to  adopt  the  Pennsylvania  measure,  which  gives  frag- 
mental, 5,010;  limestone  500. 


362  SPECIAL   PLANETOLOGY. 

UPPER  CARBONIFEROUS  series. — Maximum  tnickness  of 
Coal  Measures  in  Nova  Scotia,  14,570  feet  (in  Pennsyl- 
vania, 9,000  feet  and  over). 

Turning  next  to  the  Mesozoic  and  Tertiary  ages,  the 
following  statement  of  maximum  thicknesses  is  afforded 
by  the  most  recent  investigations. 

TRIASSIC. — Koipato  Group,  of  the  West  Humboldt 
Range,  6,000  feet,  strictly  non-calcareous.  Star  Peak 
Group,  5,300  feet  of  quartzites,  and  4,600  feet  of  lime- 
stone (King).  Total  fragmental,  11,300  feet;  limestones, 
4,500  feet. 

JURASSIC. — In  the  West  Humboldt  Range,  1,800  feet 
of  impure  limestones  and  4,000  feet  of  shales.  Say  frag- 
mental, 4,800  feet;  limestones,  1,000  feet. 

CRETACEOUS. — In  the  Uinta  region:  Dakota,  500  feet 
of  sandstones  and  clays;  Colorado,  2,000  feet  of  clays, 
marls  and  some  (say  100  feet  of)  limestone;  Fox  Hills, 
4,000  feet  of  sandstones  (King).  Total  fragmental,  6,400 
feet;  limestones,  100  feet. 

TERTIARY. — Laramie,  in  Green  River  Basin,  5,000 
feet,  mostly  sandstones.  Wahsatch,  in  Rocky  Mountains, 
5,000  feet  of  marls  and  sandstones.  Green  River,  in 
southwestern  Colorado  (Cope),  2,670  feet  of  shales. 
Bridger,  5,000  feet  of  argillaceous  and  arenaceous  strata. 
Uinta,  600  feet  of  grits  and  conglomerates,  in  Uinta  Range. 
White  River  Group,  2,000  feet  of  calcareous  clays, 
alternating  with  sandstones,  in  Wind  River  Mountains. 
Truckee  Group,  4,000  feet,  chiefly  of  indurated,  trachytic 
mud.  Loup  River  Group,  2,000  feet  of  sandstones,  on 
the  Great  Plains.  North  Park  Group,  300  feet  of  sandy 
and  marly  deposits.  Total  fragmental,  26,470  feet;  lime- 
stones, 100  feet. 

From  these  results  may  be  compiled  the  following  table 
of  maximum  thicknesses: 


THE   EARTH.  363 

Fragmental.  Limestones. 

EOZOIC 47,100  2,900 

LAUBENTIAN 27,200  2,800 

HURONIAN 19,900  100 

PALEOZOIC 75,999  12,250 

SILURIAN    37,155  11,200 

LOWER  SILURIAN 29,000  9,500 

Primordial 15,400  200 

Canadian   6,400  7,800 

Trenton    7,200  1,500 

UPPER  SILURIAN 8,155  1,700 

Niagara 6,605  100 

Salina 1,550  100 

Lower  Helderberg 1,500 

DEVONIAN 19,214  550 

Oriskany 470  50 

Corniferous 300  500 

Hamilton 6,000 

Chemung 4,900 

Catskill 7,544 

CARBONIFEROUS 19,630  500 

Lower  Carbon  if  erous 5,060  500 

Upper  Carboniferous 14,570 

MESOZOIC 22,500  5,600 

TRIASSIC 11,300  4,500 

JURASSIC 4,000  1,000 

CRETACEOUS 6,400  100 

TERTIARY 22,470  100 

Total  stratified  rocks  to  Quaternary.  .168,069  20,850 

Fragmental  and  calcareous 188,919  feet. 

To  arrive  at  a  truer  expression  of  time  ratios,  we  must 
probably  diminish  Mesozoic  fragmental  deposits  one-fifth, 
and  Tertiary  deposits  perhaps  one-half,  and  increase  all 
calcareous  strata  five-fold.  The  combined  results  give  the 
numbers  entered,  on  a  following  page,  in  the  table  of  the 
"Estimated  Length  of  Geological  Periods."  These,  for 
the  sake  of  easier  comparison,  are  reduced  to  percentages 
in  another  column. 

From  this  table  it  appears  that  the  Lower  Silurian  was 
4.6  times  as  long  as  the  Upper  Silurian;  the  Devonian 
was  nearly  one-fourth  the  duration  of. the  Silurian;  and 
the  Carboniferous  was  as  long  as  the  Devonian.  The 
Palaeozoic  was  3^  times  the  length  of  the  Mesozoic  and 
9£  times  the  Caenozoic.  The  Tertiary  was  one-ninth  of  the 
time  since  the  lower  Silurian,  while  Sir  Charles  Lyell 


364  SPECIAL   PLANETOLOGY. 

makes  it  one-fourth  the  time  since  the  Cambrian.*  Ram- 
say makes  the  Devonian  and  Triassic  united  equal  to  the 
Jurassic,  Cretaceous  and  Ca?nozoic;f  but  the  tabular 
ratios  here  determined  make  the  former  2£  times  the 
latter.  The  Tertiary,  it  appears,  was  one-sixteenth  the 
Mesozoic  and  Palaeozoic  united;  while  Professor  Dana 
makes  it  one-fifteenth. J 

With  a  view  to  arriving  at  some  absolute  measure  of 
geological  periods,  we  may  assume  Post-Tertiary  time  to 
be  one-fourth  as  long  as  Tertiary. §  We  may  also  assume 
the  Glacial  epoch  to  be  two-thirds  of  the  Post-Tertiary; 
and  may  further  assume  the  Azoic  period  of  the  earth's 
sedimentary  history  to  be  equal  to  the  Eozoic;  and  the 
pyrolithic  or  presedimentary  incrustive  history  to  be  equal 
to  the  Azoic  and  Eozoic  united,  and  here  designated 
Archaean.  We  are  thus  furnished  with  an  expression  for 
the  incrusted  age  of  the  world  in  terms  of  sediments,  and 
may,  for  convenience,  calculate  a  percentage  value  for  each 
interval  as  shown  in  one  of  the  columns  of  the  table 
referred  to.  These  are  the  final  time  ratios.  If  we  assume 
the  whole  incrusted  age  of  the  world  as  80,000,000  years, 
according  to  Sir  William  Thomson,  the  time  to  be  allotted 
to  each  period  is  such  as  shown  in  another  column  of  the 
table.  If,  again,  according  to  Professor  Newcomb,  we 
allow  10,000,000  years  for  the  time  since  sedimentation  be- 
gan, which,  calculating  from  the  tabular  time  ratios,  makes 
13,844,662  years  for  the  time  since  incrustation  began,  we 
get  the  series  of  values  given  in  the  last  column  of  the  table. 

*  Lyell :  Principles  of  Geology,  10th  ed. 

t  Ramsay,  Proc.  Roy.  Soc.,  Xo.  152,  1874. 

*He,  however,  counts  the  Laramievrith  MESOZOIC,  while  here  it  is  regarded 
as  Tertiary.  My  former  conviction*,  in  accord  with  the  views  of  Marsh  and 
Cope,  have  been  here  abandoned  in  deference  to  the  recent  positive  statements 
of  C.  A.  White.  (Amer.  Jour.  Set.,  Ill,  xxv,  207-9.) 

§Prof.  Dana  puts  the  Post-Tertiary  equal  to  one-third  of  the  Tertiary;  but 
he  does  not  include  the  Laramie  group  in  the  Tertiary,  nor  does  he  accord  the 
Tertiary  accumulations  the  enormous  thickness  which  they  have  recently  been 
shown  to  possess. 


THE   EARTH.  365 

ESTIMATED  LENGTH  OF  GEOLOGICAL  PERIODS. 


FORMATIONS. 

ROCK 

MEASURE, 

feet. 

PER- 
CENT- 
AGE. 

THOMSON'S 
BASIS, 

years. 

NEWCOMB'S 
BASIS, 
years. 

PYROLITHIC  

123  900 

27  77 

22,216.000 

3.845,000 

ARCH^AN         

1^3  ?00 

27  77 

22,216,000 

3,845,000 

Azoic    

61  600 

13  88 

11,104,000 

1,922,000 

61  600 

13  88 

11  104  000 

1  922  000 

Laurentian  

41  200 

9.26 

7,408,000 

1,282,000 

Huronian  

20  400 

4.62 

3,696,000 

639,000 

137  244 

30  93 

24  744  000 

4,282,000 

93  150 

21  00 

16  800  000 

2,907,000 

76  500 

17  25 

13  800  000 

2,388,000 

16  400 

3  70 

2  960  000 

512,000 

Canadian  
Trenton    
Upper  Silurian  .... 

45,400 
14,700 
16  650 

10.23 
3.32 
3  75 

8,184,000 
2,656,000 
3,000  000 

1,416,000 
460,000 
519,000 

^  ia^ara  

7  100 

1  60 

1,280,000 

221,000 

Salina    

2  050 

46 

368  000 

64,000 

Lower  Helderberg  . 
Devonian  

7,500 
21  964 

1.69 
4  96 

1,352,000 
3,968,000 

234,000 
686,700 

Oriskany  
Corniferous  
Hamilton  

720 
2,800 
6,000 
4  900 

.17 
.63 
1.35 
1  11 

136,000 
504,000 
1,080,000 
888  000 

23.500 
87,000 
186,900 
153  700 

Catskill  
Carboniferous  
Lower  Carboniferous. 
Upper  Carboniferous. 
MESOZOIC             .           > 

7,544 
22,130 
7,560 
14,570 
45  360 

1.70 
4.98 
1.70 
3.28 
10  22 

1,360,000 
3,984,000 
1,360,000 
2,624,000 

8  176  000 

235,400 
689,500 
235,400 
454,100 
1,415  000 

31  540 

7  11 

5  688  000 

984  400 

8  200 

1  85 

1  480  000 

256,100 

Cretaceous  

C^ENOZOIC  

Tertiary      

5,620 
14,669 
11  735 

1.26 
3.31 

2  65 

1,008,000 
2,648,000 
2,120  000 

174,400 
458,300 
366  900 

Post-Tertiary      

2,934 

66 

528,000 

91,370 

Glacial  

1,956 

44 

352  000 

60,920 

Post-Glacial  

978 

22 

176,000 

30,460 

TOTAL  CRUST  

443,673 

100.00 

80,000,000 

13,845,000 

It  can  hardly  be  doubted  that  the  total  thickness  of  the 
Laurentian  and  Huronian  series  of  strata  is  much  greater 
than  has  been  observed  or  estimated.  Few,  I  think,  would 
hesitate  to  admit  that  Eozoic  Time  was  as  long  as  Lower 
Silurian,  but  our  table  only  makes  it  about  four-fifths  as 


366  SPECIAL    PLASTETOLOGY. 

long.  It  is  not  at  all  improbable  that  some  large  portion 
of  the  primitive  strata  designated  Azoic,  as  well  as  the 
entire  Pyrolithic  crust,  has  been  removed  through  ascent 
of  the  isogeothermal  planes,  so  that  the  remaining  thick- 
ness, even  if  measurable,  would  riot  afford  a  correct  rela- 
tive measure  of  Pyrolithic  and  Archrean  time.  The  effect 
of  an  augmentation  of  Pvrolithic  and  Archaean  time  would 
be  a  diminution  of  the  relative  length  of  all  the  later 
periods.  It  may  be  mentioned,  on  the  contrary,  that 
strong  probability  exists,  as  before  shown,  that  the  accu- 
mulation of  sediments  was  more  rapid  in  primitive  times 
than  during  the  later  periods.  The  shorter  year,  the  more 
rapid  rotation  of  the  earth,  the  superior  tidal  efficiency  of 
the  moon  and  sun,  not  to  mention  more  energetic  chemical 
action,  all  disclose  the  existence  of  geological  forces  which 
must  have  acted,  in  remote  times,  with  a  degree  of  energy 
for  which  the  agencies  of  modern  times  present  no  ade- 
quate measure.  These  facts  point  toward  a  diminution  of 
the  ratios  for  remote  ages,  and  an  increase  of  those  for 
later  times.  This  would  raise  the  numerical  value  of  post- 
glacial time  above  the  figures  indicated  by  more  direct, 
and  apparently  more  trustworthy  estimates  remaining  to 
be  noticed.  The  alternative  is  therefore  to  diminish  the 
whole  time  allowed  since  incrustation  and  sedimentation 


in. 

(5.)  Calculation  based  on  the  obliteration  of  the  rota- 
tional effects  of  the  upheaval  of  a  continental  mass.  Rev. 
S.  Haughton  has  attempted  to  calculate  a  minor  limit  for 
the  time  since  the  elevation  of  Europe  and  Asia,  at  the 
end  of  the  Nummulitic  epoch.*  He  shows  that  the  uplift 
of  this  continental  mass  must  have  displaced  the  axis  of 
maximum  inertia  of  the  earth  through  sixty-nine  miles, 
in  the  direction  of  the  meridian  of  the  Andes.  The  axis 
of  rotation  would  thus  acquire  a  motion  on  the  surface  of  a 

*  Haughton:  Philosophical  Magazine,  December  20, 1877,  534-4«. 


THE   EARTH.  367 

right  cone  around  the  axis  of  figure,  with  its  pole  at  the 
distance  of  sixty-nine  miles  from  the  pole  of  the  axis  of 
figure;  and  this  motion  would  be  perpetual  unless  de- 
stroyed by  friction.  But  the  place  of  the  ocean  would 
always  be  slightly  behind  the  place  of  the  rigid  earth, 
and  some  friction  would  constantly  result,  which  would 
tend  to  destroy  the  wabbling  movement  of  the  earth.  As 
astronomy  is  now  unable  to  detect  any  such  movement, 
though  the  precision  of  its  instruments  should  detect 
a  wabble  of  five  feet  (instead  of  sixty-nine  miles),  the 
problem  is  presented,  What  time  has  been  occupied  in  the 
destruction  of  the  wabble  ?  From  researches  on  tidal  fric- 
tion,* which  causes  a  retardation  amounting  to  one  sec- 
ond in  the  length  of  the  day  in  100,000  years,  Professor 
Haughton  now  calculates  that  if  Europe  and  Asia  were 
suddenly  elevated,  a  wabble  of  sixty-nine  miles  would  re- 
quire 640,730  years  for  its  extinction.  If  they  were 
formed  by  sixty-nine  geological  uplifts,  each  of  which  dis- 
placed the  axis  of  figure  through  one  mile,  then,  supposing 
the  radius  of  the  wabble  to  be  reduced  from  one  mile  to 
five  feet  in  the  interval  between  each  two  successive  convul- 
sions, the  minimum  time  required  for  the  extinction  of  the 
wabble  would  be  27,491,000  years.  If,  again,  the  rate  of 
upheaval  of  Europe  and  Asia  was  so  slow  that  the  increase 
of  the  radius  of  an  assumed  wabble  of  five  feet  was  exactly 
destroyed  by  friction  during  each  wabble,  then  the  total 
time  required  for  the  production  of  Europe  and  Asia 
would  be  4,170,000  years.f 

*  Delaunay :  Sur  le  EalenLlssement  de  la  Rotation  de  la  Terre.    Paris,  1866. 

tit  is  erroneous  to  assume  Europe  and  Asia  produced  entirely  after  the 
close  of  the  Nummulitic  epoch.  This  mid-Eocene  disturbance  elevated  the 
Pyrenees,  the  Julian  Alps,  the  Appenines  and  Carpathians,  and  probably  ex- 
tensive regions  in  Northern  Africa,  and  through  Central  Asia  as  far  as  Japan 
and  the  Philippine  Islands.  But  large  masses  of  the  European  continent  rose 
at  intervals  during  Palaeozoic  and  Mesozoic  time.  So  that  the  period  of  the  ex- 
tinction of  the  wabble  may  have  extended  back  far  beyond  the  close  of  the 
Nnmmulitic  epoch  —  a  necessity  provided  for  in  the  second  and  third  supposi- 
tions of  Professor  Haughton. 


368  SPECIAL   PLANETOLOGY. 

Professor  Haughton  now  attempts  to  employ  the  unit 
thus  obtained  in  the  calculation  of  the  length  of  the 
earth's  sedimentary  history.  To  do  this,  he  compiles  the 
table  of  rock  thickness  before  quoted,  and  then  on  the 
principle, 

Total  sedentary  age  =  %££?££%£  X  Ttae  repre- 
sented  by  Tertiary  rocks, 

he  assumes  the  minor  limit  given  above  under  the   first 
supposition,  and  gets 

4^  X  640.730  =  11,700,000  years. 

6,000 

This  approximates  Professor  Newcomb's  calculation  of 
the  sedimentary  age  of  the  world. 

Since,  however,  it  can  hardly  be  assumed  that  Europe 
and  Asia  were  uplifted  per  saltuni,  the  above  result  for 
the  sedimentary  age  of  the  world  must  be  too  small.  If 
the  formation  of  the  continent  occupied  a  million  years, 
the  total  duration  of  sedimentary  time  would  be  nearly 
37,000,000  years.  Manifestly,  however,  the  succession  of 
uplifts  extended  back  into  Pre-Nummulitic  time,  so  that 
the  unit  obtained  cannot  be  regarded  as  representing 
Post-Nummulitic  time. 

(6.)  The  time  since  the  middle  of  the  last  glacial 
period,  based  on  the  theory  that  epochs  of  glaciation  on 
the  northern  hemisphere  have  been  caused  by  extreme 
eccentricity  of  the  earth's  orbit.  This  theory  has  been 
carefully  expounded  by  Professor  Croll.*  The  last  occur- 
ring epoch  of  maximum  eccentricity,  according  to  Stock- 
well's  calculations  f  (supplemented  by  Croll's)  were,  before 
1800  A.D.,  100,000  years,  210,000  years,  310,000  years, 
750,000  years  and  850,000  years.  Those  at  210,000  and 
850,000  years  are  the  most  striking.  Professor  Croll 
regards  the  last  glacial  period  as  extending  from  240,000 

*  Croll:  Climate  and  Time. 

tStockwell,  Smithsonian  Contributions  to  Knowledge,  x\\\\\  R.  W.  McFar- 
land,  Amer.  Jour.  Sci.,  Ill,  ?i,  456, 
24 


THE    EAETH.  369 

to  80,000  years  ago.  The  maximum  of  850,000  years,  he 
thinks,  fell  in  the  Miocene  period;  and  a  maximum  at 
2,500,000  years  ago  he  regards  as  belonging  to  the 
Eocene.  If,  according  to  Croll,  the  advent  of  the  last 
glacial  period  occurred  240,000  years  ago,  this  number 
represents  Post-Tertiary  time,  which,  according  to  the 
foregoing  table,  represents  0.4  of  one  per  cent  of  the 
whole  time  since  incrustation  began,  and  would  make  that 
time  60,000,000  years.  Again,  if  2,500,000,  according  to 
Croll,  represents  the  time  since  the  beginning  of  the  Ter- 
tiary Age,  the  whole  incrusted  age  of  the  world  would  be 
131,600,000  years,  which  I  do  not  feel  disposed  to  allow. 
If  100,000  years  be  taken  as  marking  the  middle  of  the 
last  glacial  epoch,  then  by  the  same  table  of  ratios,  the 
incrusted  age  of  the  world  would  be  33,000,000  years. 
Even  this  is  18,000,000  years  more  than  Professor  New- 
comb's  calculation  allows  when  combined  with  the  above 
tabular  ratio  for  the  Pyrolithic  Aeon. 

(7.)  Estimates  based  on  rates  of  erosions  and  deposi- 
tion. The  Niagara  gorge  has  exercised  the  wits  of  a  long 
series  of  observers.  Mr.  Robert  Bake  well  assumed  the 
rate  of  recession  to  be  three  feet  a  year,  from  which  he 
calculated  the  age  of  the  gorge,  seven  miles  in  length,  to 
be  12,300  years.*  Messrs.  Lyell  and  Hall,  assuming  a 
rate  of  one  foot  a  year,  obtained  a  result  of  35,000  years,  f 
Mr.  E.  Desor,  on  an  assumed  rate  of  .03  foot  per  annum, 
made  the  age  of  the  gorge  1,232,000  years.  Mr.  Jules 
Marcou,J  in  1863,  found  a  recession  of  twelve  feet  in  the 
Canadian  fall  at  the  base  of  the  "Terrapin  Tower,"  since 

*R.  Bakewell:  Introduction  to  Geology,  260;  London's  Magazine  of  Nat- 
ural History,  1843-4. 

tSir  Charles  Lyell,  Proc.  Geol.  Soc.,  London,  1842,  1843;  Travels  in  North 
America,  1st  Visit,  ch.  ii;  Principles  of  Geol.,  8th  ed..  205;  James  Hall,  Boston 
Jour.  Nat.  Hist.,  1843-4;  Geol.  Fourth  Dist.  New  York,  ch.  xx,  1843. 

i  Jules  Marcou,  Bulletin  de  la  Soc.  geol.  de  France,  II,  xxi,  290-300,  529,  two 
plates.  See  also  Ramsay,  Quar.  Jour.  Geol.  Soc.,  xv,  212, 1859,  who  thinks  the 
falls  commenced  during  the  deposition  of  the  "Leda  Clay,"  or  a  little  before  the 
close  of  the  Drift  period. 


370 


SPECIAL    PLANETOLOGY. 


the  trigonometrical  survey,  executed  under  the  direction 
of  Professor  James  Hall  in  1842.  This  is  a  recession  of 
.57  foot  per  annum  at  that  point,  and  implies,  if  applied 
to  the  entire  gorge,  a  period  of  64,842  years.  Mr.  Thomas 
Belt,*  after  a  careful  examination,  assumed  the  rate  of 
recession  at  .01  foot  per  annum.  But  he  announced  the 
important  discovery,  if  a  fact,  that  the  ancient  gorge, 
from  the  whirlpool  to  St.  David's,  on  the  Canadian  side, 
now  filled  with  gravel,  was  excavated  in  pre-glacial  times; 
and  the  old  gorge  apparently  extended,  also,  up  nearly  to 
the  present  falls.  In  this  view,  the  only  post-glacial  work 
is  included  between  Queenston  and  the  whirlpool,  with 
the  addition  of  an  unknown,  but  probably  small,  portion 
of  the  gorge  above  the 
whirlpool.  Mr.  Belt  as- 
sumes, however,  in  round 
numbers,  that  20,000 
years  express  the  maxi- 
mum limit  of  time  since 
the  commencement  of  the 
new  gorge  at  Queenston. 
His  own  assumption  of  the 
rate  of  recession  would 
give  for  the  three  miles  be- 
'  low  the  whirlpool,  158,000 
years,  which,  as  Mr.  Belt 
recognizes,  is  more  than 
the  time  at  our  disposal 
for  the  incrusted  history 
of  the  earth  will  allow. 
The  accompanying  dia- 
gram will  illustrate  Mr. 
Belt's  views. 

Mr.  James  T.  Gardner, 


Fl°-  53-  NlAOA 


"  °LD  AND 


*  Thomas  Belt,  Quar.  Jour,  of  Science,  April,  1875. 


THE   EARTH.  371 

Director  of  the  New  York  State  Survey,  has  given  atten- 
tion to  the  rate  of  recession  of  Niagara  Falls,  reproducing 
Hennepin's  narrative  and  illustration,  and  the  map  of  the 
triangulation  of  1842,  by  Mr.  Blackwell.*  On  the  lat- 
ter he  has  laid  down  also  the  line  of  the  falls  as  deter- 
mined by  the  United  States  Lake  Survey  in  1875.  f  From 
this  comparison  is  shown  "the  unexpected  fact  that  the  Horse 
Shoe  Falls  have  receded,  in  places,  160  feet  during  thirty- 
three  years,  and  that  a  large  island  has  disappeared  which 
formerly  existed  in  the  midst  of  the  Canadian  Rapids."  In 
spite  of  some  slight  inaccuracy  resulting  from  the  indepen- 
dent datum  points  of  the  surveys  of  1842  and  1875,  the  errors 
cannot  be  so  great,  as  Director  Gardner  informs  me,  that 
the  assumption  of  a  recession  of  100  feet  in  thirty-three 
years  would  involve  any  degree  of  uncertainty.  This  is 
an  average  of  three  feet  a  year,  and  implies  12,320  years 
for  a  gorge  seven  miles  long.  For  the  three  miles  below 
the  whirlpool,  this  rate  of  recession  requires  5,280  years, 
which,  adding  for  some  amount  of  work  above  the  whirl- 
pool, comes  strikingly  near  to  other  estimates  of  post- 
glacial time,  presently  to  be  mentioned.  At  the  same 
time,  this  is  by  far  the  most  trustworthy  determination 
ever  made  of  the  rate  of  recession  of  the  Falls. 

It  may  be  added  that  I  find  it  stated  in  the  public 
prints  that  great  changes  took  place  at  the  Falls  during 
1880,  and  these  were  especially  commented  on  at  the 
annual  meeting  of  "old  settlers."  The  Canadian  Fall  is 
said  to  have  changed  more  during  the  preceding  year 

*  J.  T.  Gardner:  Report  of  New  York  State  Survey  for  the  Tear  1879. 

tBy  a  remarkable  oversight  the  triangulation  of  the  Lake  Survey  was  not 
connected  with  the  survey  of  1842 ;  although  the  permanent  landmarks  of  the 
earlier  survey  were  perfectly  accessible,  and  such  connection  only  was  needed 
to  shed  important  light  on  a  highly  interesting  problem.  The  mutual  adjust- 
ment of  the  two  triangulations  was  made  by  Director  Gardner  in  1879;  and 
while,  as  he  writes  (Feb.  21,  1883),  the  accuracy  attainable  is  not  as  great  as  if 
the  two  triangulations  had  been  referred  to  the  same  datum  points,  it  is  safe  to 
assume  that  the  true  relative  positions  of  the  Horse  Shoe  Falls  in  1842  and  1875 
are  shown  without  a  probable  error  greater  than  twenty  feet. 


372  SPECIAL   PLANETOLOGY. 

than  during  the  twenty  or  thirty  years  previous.  The 
Fall,  "in  the  centre,  has  fallen  back  some  75  to  100  feet." 
Without  claiming  for  these  figures  any  considerable  ex- 
actness, they  may  apparently  be  received  as  evidence  of  a 
more  rapid  recession  than  most  students  of  the  Falls  have 
admitted,  and  they  are  strongly  sustained  by  Mr.  Gard- 
ner's more  scientific  determinations. 

The  gorge  of  the  Mississippi  River  below  the  Falls  of 
St.  Anthony  has  been  studied  by  Professor  N.  H.  Win- 
chell.*  This,  he  argues,  is  entirely  a  post-glacial  erosion 
as  far  as  Fort  Snelling.  The  mean  rate  from  1680  to  1856 
appears  to  have  been  5.15  feet  a  year,  so  that  the  time 
required  for  recession  from  Fort  Snelling,  eight  miles,  is 
8,202  years.  The  date  of  the  commencement  of  this  part 
of  the  gorge,  according  to  the  geological  indications,  was 
"  near  the  acme  of  glacial  cold,  or,  at  least,  when  the  effect 
of  that  cold  on  the  superficial  accumulations  was  greatest." 

Various  estimates  have  been  framed  of  the  rate  of 
deposition  in  deltas.  Elaborate  investigations  have  been 
made  of  the  Mississippi  delta  under  the  auspices  of  the 
United  States  government.  Messrs.  Humphreys  and 
Abbott,f  by  a  careful  comparison  of  the  volume  of  the 
delta  deposit  with  the  volume  of  sediment  transported 
annually  to  the  Gulf  of  Mexico,  estimate  the  age  of  the 
delta  to  be  about  5,000  years.  This,  of  course,  supposes 
uniformity  in  the  rate  of  deposition,  and  expresses  the 
time  since  the  adjustment  of  the  present  drainage  system, 
and  not  since  the  "acme  of  glacial  cold." 

Similarly,  the  age  of  the  Nilotic  delta  has  been  set 
down  at  6,350  years.J 

*N.  H.  Winchell,  Quar.  Jour.  Geol.  Soc.,  London,  Nov.,  1878,  880-901: 
Fifth  Ann.  Report  Geol.  Minn.,  1876.  See  digest  in  SonthalPs  The  Epoch  of 
the  Mammoth,  ch.  xxiii. 

t  Humphreys  and  Abbott:  Hydraulics  of  the  Mississippi,  1861.  But  see 
also  E.  W.  Hilgard,  On  the  Geology  of  Lower  Louisiana,  and  the  Rock  Salt  De- 
posit of  Petite  Anxt,  Proc.  Amer.  Assoc.,  1868,  327-40. 

J  De  Lanoye :  Ramses  the  Great. 


THE   EARTH.  373 

A  recent  writer  calculates  that  the  sediments  of  the 
three  great  rivers  of  China  would  fill  the  Yellow  Sea  and 
the  Gulfs  of  Pe-chili  and  Lian  Tung  in  24,000  years;  and 
in  36,000  years  would  extend  the  continent  to  its  ancient 
limit  at  the  129th  meridian,  and  south  to  the  29th  paral- 
lel.* 

The  rate  of  continental  erosion  and  consequent  subsi- 
dence has  been  much  studied  within  a  few  years.  The 
following  are  some  results.  The  surface  is  calculated  to 
subside  one  foot  in  the  basin  of  the  Plata  in  29,400  years ;f 
in  the  basin  of  the  Pei-ho  in  25,218  years;  J  in  the  basin 
of  the  Thames,  9,600  years;  §  in  the  basin  of  the  Danube, 
6,846  years;|  in  the  basin  of  the  Mississippi,  4,640 
years;^[  in  the  basin  of  the  Nile,  4,723  years;  in  the 
basin  of  the  Yang-tse,  3,707  years;**  in  the  basin  of  the 
Ganges,  1,751  years;f  f  in  the  basin  of  the  Rhone,  1,528 
years;**  the  Hoang  Ho,  1,464  years;§§  the  Po,  729  years ;I| 
in  the  basin  of  the  three  great  rivers  of  China,  the  Yang- 
Tse,  the  Hoang-ho  and  Pei-ho,  1,687  years.^11  The  general 
surface  of  England  and  Wales  is  estimated  to  subside  by 
erosion  one  foot  in  13,000  years,  and  the  continental  sur- 
face of  Europe  at  large,  one  foot  in  five  hundred  million 

*H.  B.  Guppy,  Nature,  xxii,  488.  Mr.  A.  Woeikoff  thinks  the  first  period 
should  be  extended  to  28,000  years.  Nature,  xxiii,  9. 

t  Higgins.    But  see  T.  M.  Reade,  Nature,  xxii,  559 ;  Guppy,  Nature,  xxiii,  35. 

J  Guppy :  loc.  cit. 

§  Geikie;  Huxley:  Physiography;  but  see  T.  M.  Reade,  Nature,  xxii,  559. 
J.  Prestwich  calculates  that  the  matters  in  solution  in  the  Thames  are  sufficient 
to  lower  the  surface  of  the  Thames  basin  one  foot  in  13,000  years.  Address  as 
President  Geol.  Soc.,  Feb. ,1872,  abstract,  Amer.  J&ur.  Sti.,  Ill,  iv,  413. 

II  Geikie:  Man.  Geol.,  ch.  xxv. 

tCroll  says  6,000  years  (Climate  and  Time,  330),  and  so  says  Geikie.  Mr. 
A.  Tylor  says  one  foot  in  10,000  years  (Phil.  Mag.,  1850). 

**H.  B.  Guppy,  Nature,  xxii,  486-8;  but  see  A.  Woeikoff,  Nature,  xxiii,  9. 

tt  Geikie  says  2,358  years  (op.  cit.),  and  so  says  Croll  ( Climate  and  Time,  331). 
See  also,  Amer.  Jour.  ScL,  III,  xii,  458. 

tt  H.  B.  Gnppy,  Nature,  xxii,  488. 

§§  Geikie. 

III!  Geikie. 

tT  Guppy.    On  river  sediments  see  Reclus :  The  Earth,  ch.  lii-iv. 


374  SPECIAL  PLANETOLOGY. 

years.*  Prof.  Croll,  on  the  basis  of  a  much  more  extended 
examination,  and  a  juster  apprehension  of  the  whole  range 
of  evidence,  concludes  that  the  general  surface  of  the  land 
is  subsiding  by  erosion  at  the  rate  of  one  foot  in  five  or  six 
thousand  years. 

It  is  manifest  that  the  action  of  water  in  lowering  the 
surface  of  the  land  is  two-fold,  mechanical  and  chemical, 
and  that  investigators  have  not  generally  taken  this  fact 
into  account,  since  they  have  studied  chiefly  the  effects  of 
erosive  action  as  revealed  in  sediments.  But  chemical 
solution,  of  calcareous  matters  especially,  amounts,  in 
some  regions,  to  almost  as  much  as  the  processes  of  sur- 
face denudation,  as  Prestwich  has  shown  for  the  basin  of 
the  Thames.  Uniting  chemical  and  mechanical  agencies, 
the  total  diminution  of  the  land  must  be  much  more  rapid 
than  is  shown  by  the  foregoing  citation  of  results. 

(8.)  The  rate  of  Bluff-recession  and  Terrace-formation. 
Professor  E.  Andrews  has  made  a  careful  study  of  the 
formation  of  the  terraces  and  sand  beaches  bordering 
Lakes  Michigan  and  Huron,  especially  in  the  neighborhood 
of  Chicago  and  the  southern  extremity  of  Lake  Michigan. f 
He  finds,  from  the  present  rate  of  erosion  (5.28  feet  per 
annum),  that  2,720  years  have  been  occupied  in  the  reces- 
sion of  the  bluffs  which  bound  the  lake  at  its  present  level. 
But  above  the  bluffs  are  two  successively  higher  sand 
beaches.  By  comparing  their  total  contents  with  the  con- 
tents of  the  modern  beach  (contemporaneous  with  the 
modern  bluff,  and  therefore  2,720  years  old),  it  appears 
that  the  two  upper  beaches  have  required  2,570  years  for 
their  accumulation.  The  sum  of  these  numbers,  5,290 
years,  represents  the  whole  time  elapsed  since  the  close  of 

*T.  M.  Reader  Address,  Liverpool  Geol.  Soc.,  1876;  Nature,  26  Oct.,  1876; 
Amer.Jour.  Sci.,  Ill,  xii,  462.  Beyond 'question,  this  is  a  most  extravagant 
estimate,  and  deserves  citation  merely  as  a  curiosity. 

t  E.  Andrews,  Trans.  Chicago  Acad.  Sciences,  ii.  See  also  digest  of  this 
memoir  in  Sonthall:  The  Epoch  of  the  Mammoth,  ch.  xxii. 


THE    EARTH.  375 

the  glacial  period.  In  other  words,  there  is  a  bluff  north 
of  Chicago  whose  rate  of  recession  has  been  ascertained 
by  observation.  The  former  position  of  the  bluff  has  been 
learned  by  soundings  in  the  lake,  and  therefore  the  whole 
volume  removed,  and  the  time  required  for  the  work.  But 
the  material  removed  has  been  redeposited  in  a  terrace  at 
the  south  end  of  the  lake,  whose  volume  has  been  meas- 
ured, and  whose  age  must  be  the  same  as  that  of  the  bluff. 
There  are  also  two  terraces  in  the  rear  of  the  bluff,  and  by 
comparing  their  volume  with  that  of  the  modern  terrace 
whose  age  has  become  known,  we  get  the  time  which 
elapsed  after  the  formation  of  the  lake  and  before  the  be- 
ginning of  bluff-erosion.  The  age  of  the  upper  terraces 
united  with  the  age  of  the  bluff  gives  the  time  since  the 
beginning  of  the  Champlain  epoch.  Dr.  Andrews  con- 
cludes finally,  that  the  true  time  must  be  somewhere  from 
5,300  to  7,500  years.  As  this,  according  to  the  table  of 
ratios  previously  given,  is  0.22  per  cent  of  the  total  time 
since  the  commencement  of  incrustation,  the  incrusted 
history  of  the  world  would  be  from  2,404,545  to  3,404,545 
years. 

It  would  not  be  surprising  if  Dr.  Andrews  had  consid- 
erably underestimated  the  original  volume  of  the  sands 
in  the  two  upper  terraces.  It  is  evidently  their  original, 
and  not  their  present,  volume  which  constitutes  a  measure 
of  the  time  of  deposition.  But,  since  their  abandonment 
by  the  lake,  they  have  been  exposed  to  all  that  wastage 
which,  as  we  have  seen,  Professor  Croll  calculates  to 
amount  to  one  foot  in  6,000  years.  That  is,  supposing 
these  upper  sands  to  have  been  exposed  6,000  years,  they 
have  lost  already  one  foot  of  their  original  depth.  Due 
allowance  for  this  wastage  would  lengthen  the  time  re- 
quired for  the  upper  beaches  by  an  important  percentage, 
raising  it,  perhaps,  nearly  as  high  as  the  figures  obtained 
for  the  St.  Anthony  gorge.  Still,  the  method  pursued  is 


376  SPECIAL   PLAXETOLOGY. 

unimpeachable,  and  the  result  must  be  regarded  as  fairly 
approximative. 

(9.)  Still  another  method  of  calculating  the  length  of 
the  last  glacial  period  has  been  suggested  by  a  passage 
in  an  address  by  Sir  William  Thomson.*  "Any  consider- 
able area  of  the  earth,  of  say  not  less  than  a  kilometer  in 
any  horizontal  diameter,  which,  for  several  thousand  years, 
had  been  covered  by  snow  or  ice,  and  from  which  the  ice 
had  melted  away  and  left  an  average  surface  temperature 
of  13°  C.,  would,  during  nine  hundred  years,  show  a  decreas- 
ing temperature  for  some  depth  down  from  the  surface; 
and  thirty-six  hundred  years  after  the  clearing  away  of 
the  ice,  would  still  show  a  residual  effect  of  the  ancient 
cold  in  a  half  rate  of  augmentation  of  temperature 
downward  in  the  upper  strata,  gradually  increasing  to  the 
whole  normal  rate,  which  would  be  sensibly  reached  at  a 
depth  of  600  metres."  Now,  all  the  northern  portion  of 
temperate  America  has  been  buried  beneath  snow  and  ice 
for  a  thousand  years  and  much  more,  during  which  a 
greatly  diminished  rate  of  augmentation  was  established; 
and,  unless  the  time  since  the  disappearance  of  the  ice  has 
been  sufficiently  prolonged  for  the  normal  rate  to  be 
restored,  there  must  still  exist  a  slower  rate  of  downward 
increase  of  temperature  under  the  surface  of  Michigan, 
for  instance,  than  under  the  surface  of  Louisiana.  If  the 
rate  of  increase  could  be  well  established  for  regions  once 
glaciated,  and  also  for  regions  not  glaciated,  the  differ- 
ence in  the  rates  would  furnish  a  datum  for  calculating, 
on  the  principles  employed  by  Sir  William  Thomson,  the 
time  since  the  uncovering  of  the  glaciated  areas.  Even 
if  no  difference  could  be  detected  between  Louisiana  and 
Michigan,  for  instance,  in  consequence  of  the  length  of 
time  since  the  disappearance  of  glaciers  in  Michigan,  there 

*8irWm.  Thomson,  Address  Brit.  Assoc.,  Glasgow,  1870;  Amer.  Jour.Sci., 
in,  xii,  340. 


THE   EARTH.  377 

might  be  a  difference  in  the  rates  in  Louisiana  and  Win- 
nepeg,  or  Norway  House  or  Fort  Churchill. 

The  best  efforts  of  science  thus  far  to  arrive  at  a  trust- 
worthy numerical  estimate  of  the  age  of  the  world  have 
been  signally  foiled  by  the  impossibility  of  obtaining  the 
value  of  certain  constant  quantities  in  the  problem.  One 
may  feel  predisposed  to  trust  preferably  the  more  mathe- 
matical methods,  or  those  based  on  radiation,  conduction 
and  condensation,  as  likely  to  furnish  the  closest  approxi- 
mation; since  those  based  on  rate  of  geological  actions 
are  liable  to  be  vitiated  by  unsuspected  and  undiscover- 
able  variations  in  the  intensity  of  the  action  —  all  the 
more  indeterminable  because  located  in  terrestrial  periods 
separated  by  so  many  revolutions  from  the  present  ob- 
served order  of  events,  which  must  furnish  us  our  only 
rule  of  measurement.  But  even  in  the  mathematical 
methods,  it  is  indispensable  to  make  enormous  assump- 
tions, with  nothing  better  than  a  general  judgment  to  be 
our  guide.  On  the  whole,  I  am  inclined  to  accord  at  least 
equal  confidence  to  the  simple  methods  which  address 
themselves  to  the  later  results  of  geological  action,  where 
the  energv  of  the  forces  must  have  been  quite  comparable 
with  the  action  of  recent  times,  which  falls  under  our 
direct  observation.  Such  methods  are  those  depending 
on  observed  and  measured  rates  of  erosion  of  river  gorges 
and  lakeside  and  seaside  bluffs.  Among  these  we  have 
four  attempts  which  may  fairly  be  regarded  as  approxi- 
mating exact  solutions.  These  are:  (1)  The  rate  of 
recession  of  Niagara  Falls,  as  lately  announced  by  Direc- 
tor James  T.  Gardner,  combined  with  the  earlier  sugges- 
tion of  Mr.  Belt  in  reference  to  the  old  gorge;  (2)  the 
rate  of  recession  of  the  Falls  of  St.  Anthony,  as  worked 
out  by  Professor  N.  H.  Winchell;  (3)  the  rate  of  recession 
of  the  lake  bluff  north  of  Chicago,  and  the  determination 
of  the  volume  of  the  upper  terraces  above  the  bluff; 


378  SPECIAL   PLA1STETOLOGY. 

(4)  the  age  of  the  Mississippi  River  delta,  as  determined 
by  Humphreys  and  Abbot.  These  four  attempts  are 
measurements  of  the  time  since  the  disappearance  of  the 
continental  glacier,  and  the  substantial  agreement  of  the 
results  adds  to  our  confidence  in  them.  The  results  are  as 
follows: 

1.  By  Niagara  Gorge 5,280  years. 

2.  By  the  St.  Anthony  Gorge 8,202  years. 

3.  By  Lake  Michigan  Bluffs 5,300  to  7,500  years. 

4.  By  the  Mississippi  River  Delta 5,000  years. 

Now,  when  we  recall  that  some  time  must  be  added  to 

the  result  from  the  Niagara  gorge  for  some  small  amount 
of  work  done  above  the  whirlpool  in  post-glacial  time; 
that  the  result  from  the  lake  bluffs  must  be  increased  in 
consequence  of  denudation  of  the  upper  terraces  since 
they  were  first  formed;  and  that  something  must  be  added, 
also,  to  the  result  from  the  Mississippi  delta,  in  conse- 
quence of  a  commencement  somewhat  later  than  that  of 
the  other  works,  it  will  appear  that  these  various  results 
are  singularly  accordant,  and  point  toward  6,000  or  7,000 
years  as  the  most  probable  interval  since  the  commence- 
ment of  the  flood  of  post-glacial  time.  If  we  assume  this 
at  6,500  years,  the  whole  incrusted  age  of  the  world  de- 
duced from  the  table  of  ratios  would  be  3,000,000  years. 

If  our  attempts  to  ascertain  the  age  of  the  world,  or 
the  duration  of  any  single  period  of  its  evolution,  yield 
only  uncertain  results,  they  suffice  at  least  to  demonstrate 
that  geological  history  has  limits  far  within  the  wild  con- 
ceptions of  a  certain  class  of  geologists.  They  show,  if 
we  may  credit  the  indications  here  regarded  most  trust- 
worthy, a  restriction  of  the  modern  epoch  within  limits 
not  exceeding  one-tenth  or  one-twentieth  the  duration 
sometimes  assigned  to  it.*  This  conclusion,  it  may  be 

*The  author  has  long  entertained  and  often  expressed  this  view.  It  has 
also  been  recently  expressed  by  Prof.  H.  Carvill  Lewis  in  a  lecture  at  the 
Franklin  Institute,  Jan.  5,  18*3.  Also  by  Prof.  G.  F.  Wright,  in  a  paper  before 
the  Boston  Soc.  Nat.  Hist.,  March  7,  1833,  noticed  in  Science,  I,  269-71. 


THE   MOOK.  379 

mentioned  incidentally,  bears  on  the  antiquity  of  the  Medi- 
terranean race,  since  it  is  generally  believed  to  have  made 
its  appearance  during  the  later  decline  of  the  continental 
glaciers.  It  does  not  concern,  however,  the  antiquity  of 
the  Black  and  Brown  races,  since  there  are  numerous  evi- 
dences" of  their  existence  in  more  southern  regions,  in 
times  remotely  pre-glacial. 

§2.     THE  MOON. 

II  manque  qnelque  chose  aux  geolognes  pour  faire  la  geologic  de  la  Lune, 
c'est  d'etre  astronomes.  •  A  la  verite  il  manque  aussi  quelque  chose  aux  astro- 
nomes  pour  aborder  avec  fruit  cette  etude,  c'est  d'etre  geolognes. — M.  FATE. 

Die  Anziehung  welche  die  Erde  an  dem  Monde  ausubt,  zur  Zeit  seiner 
ursprunlichen  Bildung,  als  seine  Masse  noch  flussig  war,  die  Achsendrehung,  die 
dieser  Nebenplanet  damals  vermuthlich  mit  grosserer  Geschwindigkeit  gehabt 
haben  niag,  auf  die  angefuhrte  Art  bis  zu  diesem  abgemessenen  Ueberreste 
gebracht  haben  musse. — KANT. 

1.  Planet ological  Retrospect. — The  moon's  volume  is 
.0203;  its  density  .6167;  its  mass  .0125,*  the  earth's  corre- 
sponding constants  being  unity.  The  relative  amount  of 
heat  originally  possessed  by  the  moon  must  therefore  have 
been  .0125;  but  its  relative  rate  of  radiation  was  .07442. 
The  relative  duration  of  corresponding  planetary  periods 
was  therefore  .1679.  That  is,  the  moon  cooled  nearly  six 
times  as  rapidly  as  the  earth,  and  its  present  stage  is  six 
times  as  far  advanced,  if  we  regard  only  the  rate  of  refrig- 
eration.! If  tne  earth's  incrustation  began  fourteen  million 
years  ago,  and  the  moon's  began  at  the  same  time,  the 
moon  reached  the  present  terrestrial  stage  eleven  and  two- 
thirds  millions  of  years  since.  The  earth  was  only  two- 

*  Or,  according  to  Newcomb,  .012279.  The  density  given  above  is  calculated 
on  the  assumption  that  the  moon  is  a  sphere  having  a  diameter  equal  to  that 
of  its  visible  disc.  But  in  fact  the  visible  disc  presents  the  least  two  of  three 
diameters;  and  hence  the  actual  density  of  the  moon  is  slightly  less  than  the 
value  given  above. 

t  From  the  formula  in  a  note  on  p.  217,  T  =  — =.ijV&65  =  1679:  and  .TgVs  = 
5.933. 


380  SPECIAL    PLAXETOLOGY. 

thirds  through  its  Pyrolithic  ^Eon.  In  truth,  however, 
according  to  our  present  reasoning,  the  moon  reached  its 
incrustive  stage  in  one-sixth  the  time  required  by  the 
earth,  reckoning  from  the  epoch  when  the  moon  separated 
as  a  distinct  mass  of  fire-mist;  and  the  lunar  stage,  corre- 
sponding to  the  present  terrestrial,  must  have  been  reached 
much  earlier  in  the  Pyrolithic  ./Eon,  and  perhaps  even  be- 
fore the  earth's  incrustation  began. 

The  earth  was  then  another  sun  to  the  supposable 
inhabitants  of  the  moon,  having  an  apparent  diameter  3£ 
times  as  great  as  the  present  sun  —  if  we  take  no  account 
of  the  earth's  greater  volume  and  the  moon's  less  distance 
in  remote  epochs.  Whatever  the  incrusted  age  of  the 
world,  the  lunar  stage  corresponding  to  the  earth's  habit- 
able condition  was  coeval  with  the  self-luminous  aeons  of 
our  planet.  By  a  simple  calculation  based  on  relative 
diameters  and  distances  of  the  sun  and  earth  from  the 
moon,  it  appears  that  at  equal  temperatures  the  earth 
would  supply  the  moon  12£  times  as  much  light  arid  heat 
as  the  sun.*  The  temperature  of  the  sun,  however,  was 
very  much  higher  than  that  of  the  earth  in  the  early 
incrustive  stage;  and  the  solar  surface  had  probably  not 
yet  withdrawn  to  its  present  distance  from  the  earth. 

If  the  moon  at  that  remote  period  had  already  attained 

*  Let  E  i  =  the  thermal  force  of  a  unit  of  surface  on  the  earth. 
Si  =  the  same  on  the  snn. 
d  =  mean  distance  of  the  sun  from  the  moon 
d'  —  mean  distance  of  earth  from  moon. 
R  =  radius  of  sun,  and  r  =  radius  of  earth. 

e  =  number  of  units  of  radiating  surface  on  the  earth's  hemisphere. 
a  =  same  on  the  sun. 

E^and^. 

Hence  the  thermal  force  of  the  earth's  hemisphere  is 

_,      „          S,*xd-'r2      ,  ill       ri 

E  =  El  *  =       d'l  R*       =  Sl  *  '   d*  '  R7- 

But  Si  sis  the  sun's  thermal  force,  and  calling  this  unity,  we  obtain 
_    din   _  (92,330,000)2  X  (3959)2 


THE   MOON.  381 

to  synchronistic  axial  and  orbital  motions  (which,  however, 
is  improbable),  it  would  result  that  one  side  was  sub- 
jected to  a  constant  radiation  of  heat  from  the  earth,  while 
at  the  oppositions,  the  same  side  received  also  the  inces- 
sant heat  of  the  sun.  Simultaneously  the  apogeal  side 
was  turned  from  the  influence  of  both  bodies.  Under 
such  circumstances  it  is  probable  that  all  water  resting  on 
the  heated  hemisphere  would  be  vaporized  and  a  portion 
of  the  clouds,  floating  to  the  cold  side,  would  be  precipi- 
tated in  fortnightly  deluges  of  rain.  During  the  next  two 
weeks,  the  deluged  side,  through  constant  exposure  to  the 
solar  heat,  must  have  been  scorched  to  such  a  degree  that 
the  atmosphere  became  burdened  with  clouds,  and  the 
satellite  was  completely  wrapped  in  vapors,  as  I  have  to 
suggest  may  be  the  condition  of  Mercury  at  the  present 
time.  Even  in  our  day,  when  the  heat  radiated  from  the 
earth  must  be  nearly  imperceptible,  the  constant  exposure 
of  one  hemisphere  of  the  moon  to  the  sun's  rays  during 
two  weeks,  alternating  with  constant  exclusion  of  solar 
heat  during  the  next  two  weeks,  may  produce,  as  has  been 
thought,  a  physical  condition  quite  difficult  to  reason  out. 
Lord  Rosse  calculated  that  the  oscillation  of  temperature 
during  a  lunation  must  be  as  much  as  500°  Fahr.  It  is  not 
impossible  that  the  actual  temperature  fluctuates  from 
two  hundred  degrees  below  zero  to  as  much  above;  though 
Professor  S.  P.  Langley's  recent  researches  on  the  absorp- 
tive property  of  the  terrestrial  atmosphere,  and  the  in- 
creased rate  of  radiation  under  diminished  atmospheric 
pressure,  reminds  us  that  thermal  vicissitudes  on  the 
moon's  surface  may  not  be  as  great  as  has  been  supposed.* 
The  fact  that  no  cloudy  vapors  are  ever  revealed  on  our 
satellite's  surface  is  sufficient  proof  that  in  its  present 
stage  it  is  destitute  of  surface  waters.  The  absence  of  all 
indications  of  water  and  an  atmosphere  is  a  circumstance 

*  See  this  subject  considered  under  the  last  head  of  this  section. 


382  SPECIAL    PLANETOLOGY 

which  would  not  at  first  be  expected  on  the  basis  of  a 
theory  which  derives  the  moon  from  the  mass  of  the  earth. 
We  must  endeavor  to  explain  it. 

M.  Saemann  suggested,  a  few  years  ago,*  that  in  the 
progress  of  cooling,  the  water  and  the  atmosphere  may 
have  entered  into  the  pores  of  the  lunar  rocks;  and  on  the 
basis  of  Durocher's  experiments  on  the  absorbent  property 
of  various  minerals,  he  made  a  rough  calculation  which 
showed  that  the  earth  will  eventually  acquire  sufficient 
porosity  to  absorb  both  the  ocean  and  the  air.f  That  the 
fluids  of  the  moon  have  thus  disappeared  seems  entirely 
reasonable  on  the  ground  of  nebular  theory;  since,  as  I 
have  shown,  the  moon's  relative  age  is  six  times  as  ad- 
vanced as  the  earth's,  while  the  progressive  cooling  of  any 
planet  constituted  like  the  earth  must  deepen  the  zone 
of  rocks  sufficiently  cooled  to  permit  water  to  occupy  its 
pores,  and  afterward  to  afford  space  for  the  entrance  of 
the  planet's  entire  atmosphere.  J 

*  Ssemann,  On  the  Unity  of  Geological  Phenomena  in  the  Solar  System, 
Bull,  de  la  Soc.  ge'ol.  de  France,  February  4,  1861  ;  translated  in  Canadian 
Naturalist,  vi,  444-51. 

t  See  this  subject  discussed  hereafter  in  Part  II,  ch.  iv. 

J  A  general  formula  may  be  readily  deduced  which,  by  the  substitution  of 
the  requisite  constants  will  apply  to  any  planet. 
LetR  =  the  radius  of  a  planet: 

r  —  the  radius  of  the  sphere  within  the  zone  whose  pores  are  capable  of 
absorbing  the  water  of  the  planet: 

i  =  the  index  of  absorption  by  volume  ;  that  is,  the  volume  of  water  absorba- 
ble  by  a  unit  of  volume  of  rock. 

W  =  the  volume  of  water  on  the  surface  of  the  planet. 

w  =  the  relative  amount  of  water  surface  on  the  planet. 

d  =  mean  depth  of  water  beneath  the  water  surface. 

Then,  disregarding  the  thin  superficial  zone  which  may  be  already  satu- 
rated with  water,  we  shall  have 


whence  r3 

Bat  since  W  =  4  IT  R2  w  d,  we  obtain  by  substitution, 


. 

4>ri 


THE    MOON.  383 

2.  Tidal  Forces  on  the  Moon. — The  tidal  protuber- 
ance upon  the  moon  must  have  presented,  in  all  stages 
of  its  evolution,  a  comparatively  enormous  development; 
and  its  influence  upon  the  moon's  physical  condition  and 
aspects  must  have  been  permanently  recorded.  As  the 
moon's  relative  mass  is  .0125,  this  fraction  represents  the 
moon's  relative  tide-producing  power  upon  the  earth. 
The  tides  on  the  moon  must,  therefore,  have  always  pre- 
sented a  development  many  times  as  great  as  the  lunar 
tides  on  the  earth.  The  problem  of  the  linear  height  of 
the  tide  produced  by  the  earth  on  the  moon  is  quite  diffi- 
cult of  solution,  but  a  few  considerations  will  show  the 
way  to  an  approximate  result.  (1)  The  height  of  the  geal 
tide  on  the  moon  must  be  a  direct  function  of  the  relative 
mass  of  the  earth.  (2)  It  will  be  in  the  inverse  ratio  of  the 
radii  of  the  earth  and  moon,  since  we  may  here  assume 
that  the  same  tidal  force  acting  on  larger  and  smaller 

If  i*  =  radius  of  the  sphere  within  the  zone  capable  of  absorbing  both  water 

and  air, 
A  =  volume  of  the  atmosphere  reduced  to  its  density  at  the  surface  of  the 

planet,  and 

a  -  relative  volume  of  the  atmosphere,  that  of  the  planet  being  unity. 
Then  -  n  R»  -  J  n  r'*  =  W  +  A. 


And  r" 

But  A  =  |  «•  R*  X  a,.'.  |A  =  «*?,  ftnd  Sub8tituting) 


If  D  =  the  depth  to  which  the  planetary  crust  is  already  saturated  with 
water,  then 


And 


in  which  D  =  p  (f  —  t)  -\-  c,  where  p  =  rate  of  increase  of  temperature  down- 
ward ;  that  is,  number  of  feet  or  other  dimension  to  one  degree  of  increase  ; 
c  =  depth  from  surface  to  constant  temperature  ;  i  =  constant  temperature  at 
depth  c,  and  V  -  temperature  at  which  water  passes  into  steam. 


384  SPECIAL   PLANETOLOGY. 

bodies,  with  other  conditions  the  same,  produces  prolate- 
ness  of  the  same  eccentricity  in  the  two  bodies.  (3) 
Other  things  being  the  same,  the  height  of  the  geal  tide 
on  the  moon  will  be  directly  as  the  force  of  gravity  on  the 
earth  or  inversely  as  that  on  the  moon.  In  other  words, 
the  geal  tide  on  the  moon  will  be  about  eighty  times  higher 
than  the  lunar  tide  on  the  earth  in  consequence  of  the 
earth's  superior  mass;  and  six  times  as  high,  in  conse- 
quence of  the  moon's  inferior  gravity  at  its  surface;  and 
it  will  be  one-fourth  as  high  in  consequence  of  the  moon's 
smaller  size.*  The  product  of  these  factors  gives,  roughly 
speaking,  a  geal  tide  on  the  moon  about  120  times  as 
high  as  the  lunar  tide  on  the  earth. 

I  have  already  expressed  the  opinion  that  the  deforma- 
tion of  the  solid  or  incrusted  earth  through  lunar  tidal 
influence,  probably  reveals  its  existence  in  increase  of 
volcanic  and  seismic  phenomena  at  the  epoch  of  lunar 
syzygies,  and  perhaps  even  in  nearly  the  whole  amount  of 
internal  heat  existing  in  the  earth.  From  this  point  of 
view,  volcanic  and  seismic  phenomena  must  always  have 
been  many  times  more  violent  on  the  moon  than  on  the 
earth. 

*  That  is,  in  general  terms,  t  =  T  .  **  .  -  .  ?    (see  also   general  formula, 
m     R    g' 

p.  229),  where  M  andm  —  the  masses  of  two  planets, 

T  and  t  =  the  heights  of  the  tides  borne  by  them  respectively, 
R  and  r  =  their  radii, 

g  and  g'  =  the  force  of  gravity  on  their  surfaces  respectively. 
Taking  the  values  for  the  earth  and  moon  from  the  Encydopcedia  Brit., 


whence  t  =  134  T. 

This  result  is  sufficiently  in  accord  with  a  remark  of  M.  Faye  (Annuaire, 
1881,  p.  721).  "La  mare"e  terrestre,  compte'e  a  partir  duniveau  moyen  desmers, 
est  de  Om.37.  La  maree  lunaire  devait  etre  de  40m  et  meme  plus.'"  Now  |« 
=  108.  M.  Faye  adds  in  a  note.  "Si  Ton  pouvait  tenir  compte  de  la  faible'sse 
de  la  densite  moyenne  de  la  Lnne,  etde  ses  dimensions  primitives,  plus  grandes 
alors  qu'aujourd'hui,  on  tronrerait  probablement  plus  de  40m.''  The  method 
of  calculation  given  in  this  note  makes  it  .37™  X  134  =:  49m  58.  If  we  take  the 
relation  given  in  the  text  it  is  .37™  X  120  =  44'".  4. 
25 


THE    MOON.  385 

3.  Physical  Aspects  of  the  Moon. —  To  render  intel- 
ligible any  reasoning  respecting  the  physical  history  of 
later  stages  of  the  moon,  it  is  desirable  to  offer  a  few 
explanations  of  the  aspects  of  the  lunar  surface.  To  the 
unaided  eye,  the  distribution  of  light  and  shade  presents 
a  configuration  which,  from  the  time  of  Plutarch,  has  been 
likened  to  the  face  of  a  man,*  and  which,  by  Helvetius,  was 
regarded  as  a  water  surface,  the  various  divisions  of  which 
have,  by  later  selenographers,  been  designated  seas,  lakes 
and  bays.  The  unaided  eye  also  discerns  some  regions  of 
peculiar  brightness,  and  even  some  radial  arrangements  of 
bright  and  dark  lines,  as  well  as  indications  of  a  very 
complicated  detail  of  structure  in  all  parts  of  the  sur- 
face. By  means  of  optical  instruments  all  these  features 
are  brought  into  wonderful  distinctness.  The  study  and 
mapping  of  the  moon's  surface  have  been  pursued  by 
modern  selenographers  with  great  assiduity,  so  that  at  the 
present  time  we  have  maps  and  descriptions  of  all  parts  of 
the  lunar  disc  as  detailed  and  exact  as  of  any  region  of 
the  terrestrial  surface.  Professor  J.  F.  Julius  Schmidt 
completed,  in  1874,  a  map  of  the  moon,  on  which  he  had 
labored  for  thirty-five  years,  and  on  which  he  had  laid 
down,  as  the  result  of  exact  triangulations,  the  altitudes 
of  3,000  mountains,  the  position  and  form  of  250  hills, 
35,000  craters,  and  an  immense  number  of  minor  features,  f 
These  studies,  together  with  those  of  Lohrmann,  Gruit- 
huisen,  Beer  and  Maedler,  Nasmyth,  Neison  and  others, 
have  given  us  lunar  positions  which,  in  the  central  parts 
of  the  moon's  disc,  cannot  be  in  error  over  3,000  feet, 
while  the  altitudes  of  the  mountains  are  exact  within  100 
feet.J  Besides  the  results  of  triangulations,  we  possess 

*  Plutarch :  De  Facie  in  Orbe  Lunce. 

iVierteljahresschrift  der  Astronomischen  Gesellschaft,  Leipzig,  ix.  232-6. 

$  "  We  have  a  better  map  of  the  moon's  surface,''  says  Professor  Lewis 
Boss,  of  the  Dudley  Observatory,  "  than  of  the  State  of  New  York  "  (Report 
New  York  State  Survey  for  the  year  1977,  p.  20) ;  and  this  statement  is  true  of 
the  whole  territory  of  the  United  States. 


386 


SPECIAL   PLAN-ETOLOGY. 


the  beautiful  photographs  of  the  moon,  executed  by 
Rutherford,  de  la  Rue  and  Draper;  and  these  show  cer- 
tain features  more  distinctly  than  direct  telescopic  vision. 
Selenographers  arrange  the  features  of  the  moon's  disc 
under  three  general  heads,  Plains,  Craters  and  Mountains; 
but  the  last  two  designations  must  be  understood  in  a 


FIG.  54.— THE  MOON. 

[Telescopically  inverted.    Hence  the  top  is  south,  the  bottom  north,  the 
right  hand  east  and  the  left  hand  west.] 

1.   Tycho,  11.  Mare  Tranquillitatls, 


2.  Copernicus, 

3.  Kepler, 

4.  Aristarchus, 

5.  Theophilus, 

6.  Ptolemseus, 

7.  Bullialdus, 

8.  Linnts 

9.  Hyginus, 

10.  Mare  Serenitatis, 


Fuecunditatis, 

Nectaris, 

Crisium, 

Frigoris, 

Iinbrimn, 

Nubium, 

Humorum, 


19.  Oceanus  Procellarum. 


special  sense,  and  not  as  expressing  any  close  analogy 
with  terrestrial  features.  The  plains  occupy  over  half  of 
the  lunar  disc.  Most  of  them  are  dark  and  well  denned, 


THE    MOON".  387 

while  the  remainder  are  light  and  undefined.  The  craters 
are  divided  into  nine  classes,  and  the  mountains  into 
twelve,  but  these  numerous  modifications  need  not  be  men- 
tioned here. 

In  general  character,  all  the  principal  craters,  so-called, 
present  a  sub-circular  form,  surrounded  by  a  rampart 
which  slopes  gently  outwards,  but  descends  precipitously 
on  the  inside  to  a  depth  considerably  below  the  general 
level  of  the  lunar  surface.  In  the  centre  of  the  crater 
exist  one  or  more  mountain-like  masses,  which  never  rise, 
however,  to  the  level  of  the  surrounding  rampart,  and 
stand,  generally  in  complete  isolation  from  it.  The  verti- 
cal configuration  of  the  crater  will  be  better  understood 
from  the  accompanying  section  through  the  crater  Coper- 
nicus—  more  accurately  styled  a  circle  or  walled  plain. 


Fi«.  55.— SECTION  ACROSS  THE  CRATER  COPERNICUS. 

The  features  here  shown  are  of  grand  dimensions.  The 
diameter  is  56  miles,  the  crest  of  the  crater  2,600  feet 
above  the  general  surface,  and  11,300  feet  above  the  bot- 
tom of  the  crater.  The  bottom  is,  therefore,  about  8,700 
feet  below  the  general  level.  This  depression  of  the 
interior  is  a  uniform  character  of  the  craters  or  circles, 
and  is  especially  marked  in  the  smaller  ones.  The  de- 
pressed bottom,  moreover,  as  Sir  John  Herschel  has 
remarked,  is  not  a  right  plane,  but  presents  a  curvature 
conformable  to  that  of  the  lunar  surface,  as  if  the  matter 
had  assumed  form  in  a  fluid  state  under  the  action  of 
gravity.  The  central  peak  often  rises  to  the  height  of 


SPECIAL   PLASTETOLOGY. 


28'  27"  26'  2S-  2* 


FIG  56.— MAP  OF  THE  CIUTKK  THEOPUILUS  AND  THE  SUBKOUNUINO  REGION.* 


'From  Xoison:  Der  Mond. 


THE   MOOH.  389 

5,000  or  6,000  feet,  but  generally  the  central  mass  or 
masses  is  much  less  elevated.  The  surrounding  rampart 
presents  a  succession  of  somewhat  concentric,  interrupted, 
terrace-like  formations,  as  if  produced  by  successive  over- 
flows of  lava  which  have  subsequently  been  disrupted  and 
eroded  in  deep  valleys.  These  characters  are  well  illus- 
trated in  the  accompanying  map  of  the  circle  or  crater 
Theophilus.  This  walled  area  is  64  miles  in  diameter, 
bounded  bv  steep,  lofty  and  variously  terraced  walls, 
which  attain  the  remarkable  elevations  of  14,000,  16,000, 
17,000  and  18,000  feet,  as  if  the  mountain  masses  of 
Mont  Blanc,  the  Jungfrau,  the  Matterhorn  and  Monte 
Rosa  had  been  piled  around  the  valley  of  Switzerland. 
The  general  crest  of  the  rampart  is  3,200  feet,  or  prob- 
ably higher,  above  the  surface  of  the  Mare  Tranquillitatis. 
In  the  interior  is  a  mountain  cut  by  deep  valleys  into 
several  separate  masses,  the  highest  of  which  is  elevated 
6,400  feet  above  the  floor.  From  the  bounding  wall 
extends  a  lofty  ridge  about  80  miles  across  the  Mare  Nec- 
taris.  North  of  Theophilus  stretches  the  Mare  Tranquilli- 
tatis, which  is  diversified  with  numerous  ridges  and  hill- 
ranges,  radiating  from  Theophilus,  and  distinguished  from 
the  dark  plain  by  their  intenser  light. 

Tycho  is  another  walled  plain  or  vast  sunken  amphi- 
theatre fifty-four  miles  in  diameter.  It  is  surrounded  by 
a  rampart  sculptured  in  numerous  terraces  on  the  inner 
side,  and  which  consists  on  the  outer  side  of  a  mass  of 
terraces  and  buttress  walls,  rising  on  the  west  17,000  feet 
above  the  central  floor,  and  on  the  east  16,000  feet,  while 
the  central  mountain  attains  an  elevation  of  6,000  feet. 
The  inner  terraces  are  cut  by  deep  gorges,  and  seem  to 
bear  some  small  craters.  The  outside  of  the  rampart  pre- 
sents an  irregular  structure,  and  assumes  the  aspect  of  a 
confused  mass  of  mountains.  The  region  more  remote  is 
crowded  with  mountains,  walled  plains  and  crater-like 


390  SPECIAL   PLANETOLOGY. 

depressions  and  pits  —  the  last-mentioned  in  countless 
numbers.  Tycho,  like  Copernicus  and  Kepler,  is  the  cen- 
tre of  a  conspicuous  system  of  light  streaks  radiating  in 
all  directions  and  spreading  themselves  over  a  fourth  part 
of  the  moon's  visible  hemisphere.  These  cross  indis- 
criminately all  the  other  accidents  of  the  surface  —  plains, 
craters,  mountains  and  valleys.  They  are  not  seen  best, 
like  the  other  features  of  the  disc,  by  oblique  light,  but 
are  most  distinct  at  full  moon,  and  a  few  of  the  intensest 
can  be  distinguished  when  merely  illuminated  by  light 
reflected  from  the  earth.  These  bands  are  from  ten  to 
twenty  miles  wide,  and  stretch  from  600  to  700  miles, 
while  one  of  them  crosses  nearly  the  whole  visible  hemi- 
sphere of  the  moon  —  a  distance  of  about  2,000  miles. 
The  light  of  these  streaks  obscures  many  important  struc- 
tures in  the  surrounding  region.  Similar  light  streaks, 
less  extensively  developed,  radiate  from  Copernicus,  Kep- 
ler, Byrgius,  Aristarchus  and  Olbers,  and,  to  a  still  smaller 
extent,  from  numerous  other  centres,  especially  between 
the  equator  and  13°  north  latitude.  It  is  a  curious  fact 
that  the  distinctness  of  all  these  streaks  is  increased  by 
photography. 

Besides  these  enormous  walled  areas,  we  find  a  multi- 
tude of  smaller  ones  ranging  down  to  a  diameter  of  four 
or  five  miles;  and  also  numerous  still  smaller  formations 
of  bright,  circular  outline,  and  steep,  massive  walls  bound- 
ing depressions  sometimes  but  half  a  mile  in  diameter. 
Finally,  to  this  class  belong  also  verv  numerous,  small, 
isolated  conical  mountains  or  hills,  from  half  a  mile  to  two 
or  three  miles  in  diameter,  having  real  crater-like  pits  in 
their  summits.  They  occur  on  the  crests  of  mountain 
masses,  on  the  slopes  of  larger  craters,  on  the  ramparts 
encircling  ringed  areas,  and  in  the  bottoms  of  these  sunken 
areas. 

One  further  class  of  structures  requires  mention.  These 


THE   MOOX.  391 

are  furrows  or  clefts  in  the  surface  —  long,  narrow,  deep 
gorges  or  fissures,  extending  generally  in  right  lines, 
sometimes  branched  or  bent,  and  sometimes  intersecting 
each  other.  They  occur  abundantly  on  the  open  plains 
without  distinguishable  beginning  or  end.  They  often 
pass  through  the  middle  of  a  mountain,  or  stretch  from  a 
crater  into  the  surrounding  plain.  In  other  cases,  they 
form  a  complicated  net-work  around  some  structure,  or 
intersect  the  depressed  floor  of  one  of  the  larger  crater 
forms.  It  is  thought  that  not  less  than  one  thousand  of 
these  clefts  have  been  laid  down  on  the  maps,  and  some  of 
them  attain  a  length  of  200  to  300  miles.  The  two  bound- 
ing walls  are  alike  and  generally  rough,  so  that  in  some 
instances  the  cleft  has  the  appearance  of  a  chain  of  craters. 
The  bottom  of  the  cleft  presents  also  a  rugged  aspect. 

The  description  of  these  voiceless  lunar  solitudes,  with 
their  weird  and  grandiose  features,  cannot  but  awaken 
interest  and  excite  the  imagination.  The  scene  is  a  wil- 
derness of  rocks  and  rents  and  pinnacled  mountains  and 
yawning  pits.  The  sun  rises  on  them  slowly  at  the  end  of 
a  fortnight  of  darkness,  and  his  steady  ray  dispels  the 
fierce  cold  of  the  departing  wintry  night.  But  no  stir  of 
conscious  activity  responds  to  day  dawn,  no  bird  of  song 
rises  on  joyous  wing  to  greet  the  rising  sun.  No  murmur 
of  a  freshening  breeze  is  heard  among  the  tree  tops,  and 
no  rippling  rill  prolongs  its  cheerful  babbling  down  the 
rugged  cleft  in  the  mountain.  The  steady  glare  of  sun- 
light warms  the  herbless  and  soilless  surface,  but  no 
vapors  rise  to  gather  in  a  summer  cloud.  The  wide  area 
is  lifeless,  noiseless  and  motionless.  This  is  the  land  of 
death.  The  mountains  sleep  in  death,  still  lifting  their 
dead  and  rigid  forms  to  dizzy  altitudes  above  the  surface 
of  a  dead  planet.  The  very  pits  sunken  by  thousands  all 
over  the  convexity  of  the  lunar  world  look  like  the  col- 
lapsed sepulchres  of  a  vast  and  neglected  cemetery.  The 


392  SPECIAL   PLANETOLOGY. 

rocky  ramparts  which  rise  upon  the  borders  are  the  monu- 
mental stones  which  mark  the  tombs  of  all  the  life  which 
once  dwelt  upon  a  planet,  and  the  thousand  rifts  in  the 
solid  floor  commemorate  the  throes  of  the  expiring  world 
itself. 

Yet  possibly  faint  indications  of  change  still  manifest 
themselves  in  this  planetary  corse.  But  they  are  the 
changes  of  disintegration  and  decay.  The  prolonged  and 
unclouded  intensity  of  the  solar  rays  succeeding  the  in- 
tense cold  of  the  bi-weekly  night  would  cause  expansions 
and  contractions  of  the  rocky  surfaces  and  rock-masses, 
which  would  impair  their  cohesion  and  weaken  the  sup- 
ports of  cliffs  and  walls.  Students  of  the  moon  have 
occasionally  fancied  that  certain  changes  had  been  noted. 
The  little  crater  Linne,  in  the  eastern  part  of  the  Mare 
Serenitatis,  has  been  an  object  of  intense  interest  in  con- 
sequence of  apparent  variations  in  its  aspects.  It  was 
first  indicated  by  Riccioli.  Lohrmann  reported  it  4^  miles 
in  diameter,  very  deep,  and  under  all  illuminations  dis- 
tinctly visible.  Miidler  found  it  6.4  miles  in  diameter.  In 
1866  Schmidt  announced  that  the  crater  had  wholly  dis- 
appeared, thoug-h  he  had  previously  observed  it  as  having 
a  diameter  of  seven  miles,  and  a  depth  of  at  least  1000 
feet.  Many  observations  were  now  made  by  others.  In- 
stead of  Linn6  a  white  spot  was  found  in  nearly  the  same 
place,  as  supposed.  Soon  Schmidt  noticed  a  little  moun- 
tain in  the  middle  of  it,  and  later,  several  observers  noted 
a  circular  depression  in  it,  about  six  miles  in  diameter, 
while  Secchi  reported  a  crater  half  a  mile  in  diameter  in 
the  middle  of  the  white  spot.  During  1867,  a  slight  de- 
pression was  reported  by  some  observers,  and  a  crater-like 
pit  by  more.  It  was  set  down  as  not  over  one  and  a  half 
miles  in  diameter.  Huggins  made  it  two  miles,  and  Buck- 
ingham, a  little  later,  three  miles,  outside  measure.  Dur- 
ing 1868,  the  object  was  much  studied,  and  it  was  generally 


THE    MOON.  393 

admitted  to  possess  the  appearance  of  a  crater-like  depres- 
sion having  an  outside  diameter  of  about  seven  miles,  with 
a  distance  of  three  miles  across  from  crest  to  crest,  a  depth 
of  not  over  500  feet,  and  a  small  central  cavity  less  than 
half  a  mile  in  diameter.  This  general  appearance  has  con- 
tinued to  the  present. 

The  reality  of  these  apparent  changes  has  been  much 
discussed.  There  are  indications  so  strong,  however,  that 
different  observers  have  not  had  their  attention  upon  the 
same  object,  that  a  definite  conclusion  is  unfortunately  im- 
possible. "  Changes  have  actually  occurred,"  says  Neison, 
"or  the  description  by  Lohrmann  and  Mjidler,  as  well  as 
Schmidt's  first  declaration,  was  erroneous,  since  so  great 
a  change  could  be  ascribed  neither  to  variations  of  libra- 
tion  nor  of  illumination."* 

The  double  crater  Messier  may  also  be  mentioned  as 
one  in  which  changes  are  by  some  believed  to  have  taken 
place  in  the  relative  size  of  the  two  craters. 

Meantime  another  supposed  change  has  been  reported,  f 
Hyginus  is  a  deep  crater  3.7  miles  in  diameter,  intersected 
by  a  cleft  1,500  yards  wide,  running  northeast  65  miles, 
and  continuing-  southwest  until  its  total  length  reaches  150 
miles.  Hyginus  and  the  region  about  had  been  many 
times  mapped  and  described  before  1877,  and  no  crater 
had  been  noted  in  all  the  neighborhood.  But  Dr.  H.  J. 
Klein,  in  May,  1877,  reported  in  the  region  north  of 
Hyginus,  a  large  dark  crater  without  a  surrounding  wall, 
but  full  of  shadows.  In  June,  he  announced  a  dark  en- 
circling band  which  on  the  next  day  had  disappeared. 
During  some  months  following,  the  indications  of  a  crater 
became  more  uncertain,  and  March  8,  1878,  they  had 

*  Nelson:  Der  Mond  und  die  Beschaffenheit  und  Gestaltung  seiner  Oberflache, 
p.  133.  A  German  translation  of  an  English  work  which  seems  to  be  out  of 
print. 

t  Neison,  Astronomical  ltegister,xvn,  Nos.  201-3,  213.  Also,  "Anhang-'of 
Der  Mond,  417-40. 


394  SPECIAL    PLANETOLOGY. 

entirely  disappeared.  On  the  seventeenth,  however,  the 
crater  was  again  distinctly  visible.  Since  that  date  a 
multitude  of  observers  have  testified  to  its  existence,  and 
it  now  occupies  a  place,  as  Hyginus  N,  which  a  score  of 
competent  selenographers  declare  to  have  been  destitute 
of  any  such  form  previously  to  the  year  1877.  In  view  of 
all  the  observations,  Neison,  who  has  systematically 
studied  them,  concludes  that  the  observations  made, 
especially  during  1879,  have  rendered  it  probable,  in  the 
minds  of  most  selenographers,  "  that  finally,  a  real  case  of 
physical  change  upon  the  moon's  surface  has  been  practi- 
cally demonstrated."  * 

Still  more  recently  we  receive  reports  of  apparent 
changes  in  the  crater  Plato.  Mr.  A.  Stanley  Williams 
writes  that  of  thirty-seven  spots  seen  in  the  crater  in 
1869-71,  six  were  not  seen  in  1879-82;  while  seven  not 
seen  during  the  first  period  were  seen  in  the  second.  The 
mean  visibilities  of  most  of  the  spots  observed  in  both 
series  agree  very  closely,  but  eight  show  a  decided  varia- 
tion in  brilliancy.  Among  the  light  streaks  in  the  crater 
some  change  was  noted,  particularly  in  one  which  was  not 
seen  at  all  during  the  first  twelve  months  of  the  first 
period,  and  is  now  larger  and  brighter  than  others  pre- 
viously observed.! 

Most  of  those  who  have  admitted  the  reality  of 
changes  in  the  lunar  craters  have  been  inclined  to  ascribe 
them  to  a  volcanic  origin;  but  others  have  very  reason- 
ably questioned  the  validity  of  such  a  conclusion.  The 
only  supposable  cause  for  such  changes  is  the  disintegra- 
tion resulting  from  the  extreme  fluctuations  of  tempera- 
ture already  referred  to.  J  These  might  effect  the  levelling 
of  crater  walls,  and  the  partial  filling  of  the  cavity,  if  of 

*  Nelson:  Der  Mond,  440. 

'(Science,  i,  311,  Apr.  20,  1883,  from  Observ.,  March  1. 

t Proctor:  The  Moon,  380-2. 


THE    MOON.  395 

small  dimensions;  but  it  is  difficult  to  conceive  of  changes 
thus  originated  as  resulting  in  the  obliteration  and  reap- 
pearance of  the  crater  Linne,  the  variations  in  the  relative 
diameters  of  the  craters  Messier,  or  the  complete  creation 
of  the  well  defined  crater  Hyginus  N.  Much  allowance 
must  be  made  for  the  changing  aspects  of  lunar  objects 
under  different  kinds  of  illumination,  much  for  the  influ- 
ence of  the  terrestrial  atmosphere,  and  much  for  the  vari- 
ous degrees  of  excellence  in  telescopes  and  the  eyesight 
of  observers.  When  all  these  deductions  are  made,  per- 
haps the  greatest  actual  changes  noted  will  not  be  found 
to  surpass  the  probable  results  of  rock  disintegration 
under  extreme  fluctuations  of  temperature. 

The  facts  thus  cited  concerning  the  topograpny  of  the 
moon,  make  it  clear  not  only  that  the  physical  conditions 
of  the  surface  of  that  planet  differ  extremely  from  those 
of  the  earth,  but  also  that  its  evolution  has  pursued  a 
widely  different  course.  We  are,  perhaps,  in  a  position 
to  reason  out  with  a  fair  degree  of  probability  the  vicissi- 
tudes of  the  moon's  physical  history. 

4.  Tidal  Evolution  of  the  Moon.  —  Adopting  the 
theory  that  the  moon  parted  from  the  earth  as  a  ring  of 
fire  mist  and  aeriform  matter,  and  underwent  spheration 
in  the  manner  heretofore  described,  it  becomes  eminently 
probable  that  its  axial  rotation  was  not,  at  first,  coinci- 
dent with  its  orbital  revolution.  The  tidal  influence  of 
the  earth,  however,  caused  the  moon  to  assume  the  form 
of  a  prolate  spheroid,  having  its  longer  axis  directed  con- 
stantly toward  the  earth,  or  very  nearly  so.  But,  as  the 
moon,  by  hypothesis,  presented  different  sides  successively 
toward  the  earth,  different  portions  of  its  substance  suc- 
cessively underwent  elevation  into  the  tidal  swell,  and 
successively  subsided  at  the  ebb.  Had  the  substance  of 
the  moon  at  this  time  been  a  perfect  fluid,  the  tidal  rise 
would  have  responded  instantly  to  the  terrestrial  attrac- 


396  SPECIAL    PLANETOLOGY. 

tion,  and  the  summit  of  the  tidal  swell  would  have  been 
directed  always  exactly  toward  the  earth.  But,  as  the 
substance  of  the  moon  was  not  a  perfect  fluid,  internal 
molecular  resistances  retarded  the  response  to  the  earth's 
influence,  and  .the  tidal  culmination  was  always  a  little 
behind  the  zenith  position  of  the  earth.  In  other  words, 
the  prolate  axis  formed  a  small  posterior  angle  with  the 
line  joining  the  centres  of  the  moon  and  the  earth.  The 
value  of  this  angle,  or  the  lagging  of  the  g-eal  tide,  would 
be  inversely  as  the  fluidity  of  the  moon's  substance.  The 
vertical  dimension  of  the  geal  tide,  notwithstanding  its 
large  absolute  value,  is  so  small  compared  with  the  diame- 
ter of  the  moon,  and  a  fire-mist  substance  possesses  so 
high  a  degree  of  internal  mobility,  that  it  is  highly  im- 
probable that  the  lagging  of  the  geal  tide  amounted  to 
any  considerable  influence  toward  the  retardation  of  the 
moon's  rotation.  Nevertheless,  it  must  have  acted  as  a 
real  retardative  cause  on  the  moon's  rotary  velocity,  and 
all  the  more  so  when  the  volume  of  the  moon  was  greater 
than  at  present,  and  its  distance  from  the  earth  Avas  less. 
In  the  course  of  time,  according  to  our  conception,  the 
matter  of  the  moon  had  cooled  to  the  condition  of  a 
liquid  globe.  The  tidal  swell  was  now  reduced  in  alti- 
tude, but  the  internal  mobility  of  its  parts  was  diminished. 
The  angle  of  lagging  was,  therefore,  considerably  in- 
creased, and  the  tangential  component  *  of  the  earth's 
attraction  on  the  tidal  protuberance  operated  more  effec- 
tively as  a  retarding  force.  At  the  same  time,  any  lack  of 
homogencousness  in  the  density  or  viscosity  of  the  parts 
would  cause  frictional  resistances  which,  precisely  on  the 
principle  of  continental  resistances  to  terrestrial  tides, 
must  have  added  something  to  the  causes  retarding  the 
moon's  rotation.  Still,  the  geal  tide  was  so  small  com- 

*  The  reader  will  recall  the  exposition  in  a  previous  section  (Part  II,  chap. 
H,  §  6.) 


THE    MOOJf.  397 

pared  with  the  mass  and  volume  of  the  moon,  that  the 
primitive  rotation  of  that  body  was  very  slowly  dimin- 
ished. Had  the  moon  suddenly  become  rigid,  its  prolate 
form  would  never  have  reduced  its  rotation  to  synchro- 
nism with  its  revolution,  since  if  the  prolate  axis  could  be 
once  moved  far  enough  to  make  an  angle  a  little  exceed- 
ing 90°,  with  the  line  joining  the  moon  and  earth,  the  polar 
protuberances  would  induce  as  much  accelerative  action 
as  retardative.  But  the  moon  was  not  rigid,  and  hence 
its  nearest  pole  was  continually  in  such  position  that  the 
earth's  attraction  was  continually  retardative.  During  its 
liquid  state,  therefore,  the  rate  of  rotation  must  have 
been  considerably  diminished,  though  it  is  far  from  prob- 
able that  the  synchronistic  stage  was  reached. 

At  length  followed  the  stage  of  incrustation.  Great 
complication  in  the  action  and  interaction  of  the  forces 
now  ensued.  This  is  the  chapter  of  lunar  history  whose 
records  are  preserved  in  the  strange  and  impressive  forms 
remaining  upon  the  visible  disc  of  our  satellite.  The 
presence  of  a  forming  crust  did  not  prevent  the  continu- 
ance of  the  geal  and  solar  tides.  These  continually  inter- 
rupted the  continuity  of  the  growing  film.  As  a  con- 
sequence, the  incipient  crust  became  a  floe  of  floating 
fragments  perpetually  grinding  against  each  other,  per- 
petually cemented  by  the  freezing  lava  which  rose  in  the 
chinks  and  spaces  between,  and  perpetually  disrupted  and 
rearranged  by  the  disturbances  of  the  recurring  tides.* 
But  as  soon  as  rigidity  began  to  appear  in  a  continuous 
crust,  most  important  changes  were  introduced  in  the  condi- 
tions of  tidal  action.  The  solid  film  yielded  less  readily 
than  the  liquid  beneath.  Its  rigidity  caused  it  also  to  yield 
to  a  less  extent.  From  the  first  cause  the  angle  of  lagging 

*  This  conception  of  the  influence  of  tides  during  the  incrustive  period  of  a 
planet's  life  has  been  expressed  by  me  in  Sketches  of  Creation,  1870,  p.  51,  and 
in  earlier  publications. 


SPECIAL   PLANETOLOGY. 


was  greater  in  the  crust  than  in  the  molten  core.  From 
the  second  cause  the  liquid  pressed  against  the  under  side 
of  the  crust,  tending  to  elevate  it  in  a  tide  of  the  altitude 
due  to  the  nature  of  the  liquid.  The  liquid  portion,  for 
instance,  tended  to  rise  in  a  tidal  swell  to  the  height  of  A, 
Figure  57;  but  the  more  rigid 
crust  rose  only  to  B,  and  the 
liquid  was  restrained  beneath 
it,  pressing  against  it.  This 
pressure  was  very  greatly  aug- 
mented by  the  greater  lagging 
of  the  crustal  tide.  The  mode 
of  action  is  illustrated  by  the 
adjoining  figure,  58,  where  E,  E, 
E  shows  the  direction  of  the 
earth,  A  represents  the  summit 
FIG.  57.  ACTION  or  THE  INTERNAL  of  the  crustal  tide,  with  a  lag- 
TIDE  AGAINST  THE  CUUST.  .  i  \  r\  n  j  TJ 

ging  angle  AGO,  and  B  rep- 
resents the  summit 
of  the  liquid  tide  if 
not  restrained  by 
the  overlying 
crust,  and  having 
a  smaller  lagging 
angle,  BOG.  The 
portion  of  the 
liquid  spheroid 
here  shown  exter- 
nal to  the  crustal 
spheroid  is  re- 

the    crustal    spheroid,   and  consequently 
the  force  due  to   the  earth's   attraction 
against  the  under  side  of  the  crust. 

It  would    be    impossible    that    the    rocky    lunar    crust 
should  attain,  for  a  relatively  long  time,  such  soundness 


J£ J- E 


FIG.  58.  EFFECT  OF  DISCORDANT  LAGGING  TIDES. 

strained    within 
presses  with  all 


THE   MOON.  399 

and  integrity  as  to  resist  fully  the  powerful  tendency  to 
rupture  resulting  from  tidal  actions.  The  periodical  press- 
ure exerted  from  beneath  by  the  liquid  tide  would  contrib- 
ute to  this  tendency.  Fissures,  perforations,  chasms  in 
the  crust,  would  be  certain  to  result.  Through  these  the 
pent-up  liquid  would  pour  at  high  tide,  in  lava  floods  of 
frightful  magnitude.  With  the  ebbing  of  the  liquid  tide, 
the  fluid  lava  would  retreat.  The  apex  of  the  crustal  tide 
now  arrived  and  the  crust  experienced  a  tendency  to 
remain  above  the  liquid  core.  Insufficient  rigidity  to 
stand  the  strain  would  prevent  the  development  of  any 
real  cavity  beneath,  but  the  crust  would  float  with  dimin- 
ished pressure  on  the  molten  sea,  and  the  fluid  would  be 
withdrawn  from  the  openings.  At  the  next  tide  of  the 
liquid  core,  the  matter  would  rise  again  through  the  vents 
and  renew  the  vast  overflow.  Then  it  would  again  subside 
and  the  vacated  perforations  in  the  crust  would  become 
.  yawning  pits  illuminated  by  the  glow  of  the  lava  sea  re- 
vealed at  bottom.  These  huge  suspirations  were  con- 
tinued as  long  as  a  lava  tide  remained  to  gush  through  the 
outlets  of  its  prison.  Long-repeated  overflows  of  molten 
matter  built  up  around  the  outlets  enormous  rims  of  frozen 
lava.  The  craters  attained  frightful  depths  which  were 
revealed  when  the  lava  tide  was  at  ebb.  Frequently,  after 
the  crater  rims  had  become  greatly  thickened,  the  fresh 
outflow  of  liquid  matter  ran  down  the  external  slopes  like 
watery  floods,  and  eroded  the  older  lavas  in  drainage 
gorges.  Again  and  again,  the  erosive  action  was  re- 
peated, and  the  surrounding  region  for  many  miles  pre- 
sented an  aspect  of  vast  and  long  continued  denudation. 
Here  were  deep  dark  canyons  winding  to  the  lower  levels; 
there  were  rugged  bosses  swelling  above  a  sea  of  frozen 
lava;  here  were  tower-like  outliers  of  more  ancient  lava 
deposits  which  had  escaped  denudation,  and  there  again, 
remained  mountain  masses  of  old  lava,  spreading  their 


400  SPECIAL   PLANETOLOGY. 

bases  over  many  a  square  mile,  and  lifting  their  attenuated 
summits  many  a  thousand  feet  above  the  surrounding 
region. 

It  will  be  particularly  noted  that  the  vertical  rise  of  the 
molten  tide  through  the  spiracles  in  the  crust  was  not  lim- 
ited to  the  tidal  elevation  proper  to  an  open,  unrestrained 
surface.  The  tidal  pressure  accumulated  against  the  re- 
straining crust.  The  tidal  swell,  pressed  back  beneath 
the  regions  of  unbroken  crust,  rushed  with  accumulated 
energy  through  the  narrow  vent  when  found.  It  was  like 
the  ten-fold  tidal  swell  along  the  Hoogly  or  the  Bay  of 
Fundy.  Hence  it  poured  over  the  crater  rims  in  torrents 
of  astonishing  depth.  Hence,  after  the  rims  had  been 
thickened  to  altitudes  of  thousands  of  feet,  the  rising  flood 
could  still  attain  their  summits  and  lay  down  new  deposits. 

Here  also,  are  disclosed  adequate  causes  of  explosive 
action.  Sometimes,  when  the  pressure  of  the  subjacent 
tide  had  greatly  accumulated,  the  solid  resistances  sud- 
denly gave  way.  Fragments  were  thrown  on  high  and 
columns  of  lava  ascended  probably  hundreds  of  feet,  as 
spouts  of  water  rise  at  the  end  of  a  long  "  purgatory  "  on 
a  rocky  sea-coast,  when  the  waves  roll  in  and  their  gath- 
ered force  spends  itself  in  the  free  space  above.  These 
explosive  occurrences  must  have  scattered  many  huge 
fragments  to  great  distances  over  the  surrounding  region; 
and,  not  impossibly,  some  of  them  were  large  enough  to 
remain  visible  through  terrestrial  telescopes.  The  credi- 
bility of  sucli  occurrences  is  increased  by  the  considera- 
tion that  while  the  cohesive  resistance  of  rock  substances 
was  the  same  as  on  the  earth,  and  the  force  of  rupture  as 
great,  the  force  of  gravitation  was  only  one-sixth  as  great 
as  on  the  earth's  surface.* 

*  The  moon's  mass  is  to  that  of  the  earth  as  0125  to  unity,  and  the  relative 
attraction  of  this  relative  mass  at  the  surface  is  inversely  as  the  squares  of  the 
radii  of  the  moou  and  the  earth.  Heiice 


THE   MOON.  401 

On  our  own  planet  there  have  been  outflows  of  molten 
matter  which  spread  themselves  in  fiery  seas  over  tens  of 
thousands  of  square  miles.  Tidal  action,  probably,  had  a 
connection  with  these  events.  On  the  moon,  where  tidal 
action  was  a  hundred  and  twenty  times  as  violent,  the 
molten  outflow  must  have  sometimes  covered  extensive 
areas,  and  cooled  into  wide  and  level  plains.  The  older 
rugosities  would  be  evenly  buried,  and  the  aspect  would 
be  that  of  an  ocean.  Here  and  there  some  of  the  greater 
saliences  caused  in  former  times  would  project  like  Alpine 
"  Grands  Mulcts,"  or  rocky  islets,  above  the  general  level. 
Over  the  stiffening  surface  fell  some  of  those  projectiles 
hurled  from  the  neighboring  craters,  and  left  their  inden- 
tations on  the  pasty  lava. 

If  the  moon  was  derived  from  the  mass  of  the  earth, 
the  constituents  of  water  and  air  must  have  belonged  to 
it,  and  it  is  eminently  probable  that  some  portions  of  these 
elements  were  left  to  enter  into  those  unions  which  form 
water  and  air.  I  cannot  entertain  the  conception  of  an 
original  destitution  of  those  substances  on  our  satellite. 
There  must  have  arrived  a  time,  therefore,  as  in  the  his- 
tory of  the  earth,  when  the  condensation  of  aqueous  va- 
pors took  place.  There  must  have  been  an  Eeonic  storm. 
The  rains  must  have  fallen  while  the  crust  was  still  in- 
tensely heated.  During  this  time  the  tidal  swells  and 
subsidences  of  the  crust  and  molten  interior  were  .punctu- 
ally alternating  with  each  other.  The  rains  were  descend- 
ing while  the  lavas  were  bursting  through  the  crater 
vents.  The  rains  descended  on  the  lava  seas.  These  me- 
teoric events  enormously  exacerbated  the  violence  of  the 
lunar  activities.  The  cooling  of  the  exposed  molten  sur- 
faces was  accelerated,  and  the  resistance  to  all  movements 

— x.JHIr.-'riV 

which  i8,  therefore,  the  moon's  relative  gravity,  the  influence  of  centrifugal 
force  being  neglected. 


402  SPECIAL  PLANETOLOGY. 

incident  to  tidal  oscillations  was  correspondingly  increased. 
Copious  volumes  of  steam  rose  and  condensed  in  clouds 
destined  to  perpetuate  the  storm  and  the  reactions  on  the 
heated  surface.  The  watery  floods  added  their  erosive 
work  to  that  performed  by  the  streams  of  lava.  Both 
kinds  of  erosion  were  enfeebled  by  the  feeble  intensity  of 
gravity  on  the  moon. 

But  meantime,  the  crust  was  thickening,  and  the  re- 
gions but  little  remote  from  the  craters  and  the  fresh  lava 
streams,  supported  accumulations  of  water.  The  water 
was  received  in  the  pores  of  the  rocks.  In  the  progress  of 
ages  the  crust  was  thickened  to  such  an  extent  that  all 
the  water  belonging  to  the  moon  had  been  absorbed. 
With  the  entrance  of  water  in  the  rocks  a  new  explosive 
agent  was  in  readiness  whenever  the  confined  lava  tides 
burst  through  new  fissures,  or  in  rising  through  the  old  ones 
encountered  watery  infiltrations.  The  crust  was  now  some 
hundreds  of  miles  in  thickness.  The  first  133  miles  would 
take  in  all  the  water  belonging  to  the  moon,  on  the 
assumption  that  its  whole  volume  bore  the  same  ratio  to 
the  volume  of  the  earth's  water  as  the  moon's  volume 
bears  to  the  earth,  and  that  the  absorbent  capacity  of  its 
rocks  was  the  same  as  that  of  terrestrial  rocks.*  It  is 
manifest,  therefore,  that  the  continued  thickening  of  the 
crust  would  increase  its  porous  capacity  to  such  an  extent 
as  to  absorb  all  the  lunar  atmosphere.  It  is  worthy  of 
special  mention  that  the  thickening  of  the  crust  upon  a 
planet  undergoing  such  copious  eruptions  of  molten  mat- 
ter, would  be  more  rapid  than  on  a  planet  comparatively 
free  from  such  eruptions.  The  increased  rate  of  .thick- 
ening would  result  both  from  the  increased  rate  of  general 
cooling,  and  from  the  addition  of  crustal  layers  upon  the 
exterior. 

*  This  results  from  an  application  of  the  formula  given  on  a  preceding  page. 
The  method  of  determining  the  constants  used  will  be  shown  when  treating  of 
the  future  stages  of  the  earth. 


THE   MOON.  403 

In  the  course  of  ages,  the  rigidity  of  the  thickened 
crust  became  greatly  increased.  It  yielded  less  to  the 
tidal  influence  and  the  lagging  angle  was  increased,  and, 
therefore,  the  still  fluid  and  tide-moved  interior  pressed 
with  increased  force  against  the  under  side.  Perhaps 
many  of  the  smaller  vents  had  become  sealed  up  in  conse- 
quence of  the  permanent  retention  and  final  solidification 
of  a  portion  of  their  lava  contents,  though  the  time  had 
not  yet  arrived  for  solidification  in  the  larger  craters. 
Perhaps  only  the  larger  vents  remained  active;  but  their 
activity  must  have  been  somewhat  enlarged.  By  and  by 
the  progressive  reduction  in  the  number  of  smaller  vents 
resulted  in  a  greatly  increased  pressure  against  the  inte- 
rior. The  thickness  and  rigidity  of  the  crust  rendered  it 
impossible  that  the  pressure  should  find  relief  in  any  new 
or  reopened  vents  of  small  dimensions.  The  pressure  was 
felt  beneath  areas  a  thousand  miles  in  diameter.  The 
whole  solid  crust  yielded.  It  rose,  uplifted  by  the  strug- 
gling, imprisoned  tide.  There  was  a  focus  of  tidal  pres- 
sure determined  partly  by  the  position  of  the  tidal  apex, 
and  partly  by  the  place  of  relative  weakness  in  the  crust. 
Here  the  supposed  lava  burst  through.  The  crust  was 
shattered  as  by  a  blow  from  beneath.  Long  radial  frac- 
tures diverged  for  hundreds  of  miles  from  the  new-made 
vent,  and  these  were  filled  by  lavas  which  were  modern  in 
Comparison  with  those  which  had  been  rent.  The  exist- 
ing accidents  of  the  lunar  surface  sustained  no  perceptible 
ratio  to  the  tremendous  power  which  had  burst  a  satellite. 
The  fractures  were  rents  in  the  general  crust.  They 
intersected  older  craters  and  mountains,  as  mere  trifling 
incidents  encountered  in  their  course.  After  the  cata- 
clysm was  past,  a  vast  system  of  radial  dykes  covered  the 
district  that  had  suffered.  In  later  ages,  the  different 
color  of  the  material,  or  the  marked  salience  of  the  dykes 
after  subsequent  erosion,  caused  them  to  appear  more 


404  SPECIAL  PLANETOLOGY. 

brightly  illuminated  than  contiguous  portions,  when  ex- 
posed to  the  solar  light  and  viewed  from  the  earth.  Some- 
what such,  perhaps,  has  been  the  history  of  those  splendid 
star  forms,  Tycho,  Copernicus,  Kepler  and  others. 

Perhaps  the  numerous  canals  or  clefts  depicted  on  the 
map  of  the  moon  belong  to  the  same  period  of  lunar 
evolution.  They  bear  an  analogy,  certainly,  to  the  great 
vein  fissures  and  trap  dykes  which  intersect  so  numerously 
terrestrial  formations  in  certain  regions.  We  may  con- 
ceive that  similar  causes  originated  them.  They  are  con- 
nected with  the  progressive  refrigeration  of  the  planet, 
the  contraction  of  its  mass,  the  unequal  strains  resulting 
from  unequal  rigidity  of  different  parts,  and  the  repeated 
stresses  created  by  tidal  oscillations. 

While  these  great  events  were  in  progress,  a  powerful 
cause  was  in  operation  destroying  the  moon's  axial  rota- 
tion. Its  action  presented  two  modifications.  First,  the 
lagging  of  the  tidal  protuberance  subjected  it  to  the  influ- 
ence of  a  horizontal  component  of  the  earth's  attraction. 
The  effect  must  be  such  as  heretofore  explained  when 
referring  to  the  earth's  diminished  velocity  of  rotation. 
Secondly,  the  retral  pressure  of  the  internal  liquid  tide 
against  the  under  side  of  the  crust,  as  illustrated  in  Figure 
57,  was  a  more  powerful  cause  of  retardation.  Finally, 
the  period  of  rotation  approximated  the  period  of  orbital 
revolution.  The  activity'  of  physical  work  upon  the  moon^ 
was  slackened.  Longer  intervals  separated  successive 
tides.  The  last  overflows  became  more  thoroughly  chilled 
and  torpid  before  new  ones  were  poured  over  them.  Now 
the  pasty  discharges  rose  slowly  to  the  crater  brim  too 
viscid  to  leave  readily  the  immediate  border,  and  thus 
added  the  last  courses  to  the  grand  rampart  whose  up- 
building had  witnessed  so  many  vicissitudes  and  so  many 
revolutions.  Probably  the  approximation  to  synchronism 
was  gradual  and  continuous.  Had  the  prolate  moon  been 


THE   MOON.  405 

rigid  and  still  destined  to  a  synchronistic  state,  there 
would  have  been  a  time  when  the  pole  of  the  longer  axis, 
after  passing  the  point  turned  toward  the  earth,  would 
have  swung  back  and  repassed  that  point  on  the  other 
side.  After  a  large  number  of  oscillations,  the  exact 
position  which  it  now  has  would  have  been  finally  as- 
sumed, and  from  that  mean  position  it  could  never  change. 
But  the  moon  was  not  completely  rigid,  and  hence  the 
rotary  motion  was  never  reversed  or  oscillatory,  and  the 
synchronistic  position  was  attained  by  progressive  differen- 
tial retardation. 

The  seen  of  lunar  violence  endured  only  while  the 
moon's  rotary  period  was  unequal  to  its  orbital  period. 
If  the  moon,  while  yet  in  a  fluid  state,  possessed  a  non- 
synchronistic  rotation,  as  in  all  probability  was  the  case, 
such  rotation  continued  long  after  the  precipitation  of 
water  upon  the  surface.  The  tidal  swell,  as  I  have  main- 
tained, would  not  tend  to  retard  rapidly  the  rotary  velocity 
of  a  planet  whose  parts  are  entirely  fluid.  But  if  one 
part  is  rigid  and  another  fluid,  or  if  one  part  is  less  fluid 
than  another,  a  relative  translation  of  fluid  parts  must 
take  place,  and  the  friction  of  fluids  and  solids,  or  of  more 
perfect  fluids  upon  less  perfect  ones,  under  the  influence 
of  a  tidally  attractive  body,  would  oppose  that  motion 
which  determines  local  translation  of  the  tidal  wave.  If 
the  rotation  is  slower  than  the  orbital  motion,  tidal  fric- 
tion will  accelerate  it.  If  the  rotation  is  faster,  it  will 
retard  it.  This  relation  of  more  and  less  rigid  parts  exists 
upon  an  incrusted  planet  having  a  molten  interior;  and 
such  a  condition  supplied,  probably,  the  principal  cause  of 
the  final  synchronistic  relation  of  the  moon's  motions. 

If  the  moon,  during  the  non-synchronistic  aeon  had 
acquired  the  condition  of  a  perfectly  rigid  or  nearly  rigid 
body,  and  possessed  at  the  same  time  a  prolate  form,  with 
the  matter  symmetrically  disposed  about  the  centre  of 


406  SPECIAL    PLANETOLOGY. 

gravity,  such  rigid  prolateness,  as  I  have  stated,  would  not 
tend  to  retard  the  axial  rotation,  but  the  satellite  would 
revolve  indefinitely  about  its  shorter  axis.  From  this  we 
infer  that  the  moon  is  not  a  rigid  body,  or  that  its  syn- 
chronistic motions  became  established  before  rigidity  was 
attained,  or  that  its  parts  were  unsymmetrically  disposed 
around  the  centre  of  gravity  in  pre-synchronistic  times. 
But  the  moon  has  never  been  a  nearly  rigid  body,  since 
the  earth  is  not  rigid,  and  the  moon  is  composed  of  the 
same  materials  in  a  lower  state  of  condensation;  and 
while  unsynchronistically  rotating,  its  parts  must  have 
been  symmetrically  disposed  about  the  centre  of  gravity, 
since  no  reason  can  be  assigned  why  they  should  be  other- 
wise; and  hence  the  establishment  of  the  moon's  syn- 
chronous motions  was  not  effected  through  the  influence 
of  an  eccentric  axis,  but  by  slow  degrees  through  the 
action  of  parts  tidally  moved  either  upon  or  beneath  the 
resisting  crust.  That  oscillation  or  libration  which  La- 
place reasoned  out  was  based  on  the  supposition  of  a  rigid 
globe,  and  it  is  not  surprising,  therefore,  that  even  with 
modern  observational  precision,  no  librations  have  been 
discovered  attributable  to  an  actual  oscillation  of  the 
prolate  axis. 

If,  after  the  synchronistic  stage  of  the  moon  had  been 
reached,  any  fluids  free  to  move,  like  water  or  air,  covered 
any  considerable  part  of  its  surface,  they  would  gather 
themselves  on  the  farther  side  of  the  moon,  since,  though 
the  centrifugal  force  is  slightly  greater  on  the  opposite 
side,  the  difference  in  the  earth's  attraction  on  the  near 
and  remoter  sides  is  about  twice  as  great  as  the  difference 
in  centrifugal  tendencies.*  The  arrangement  of  elements 

*The  centrifugal  force  on  the  farther  side  is  to  that  on  the  nearer  side  as 
1.00904  to  unity;  but  the  earth's  attraction  on  the  nearer  side  is  to  that  on  the 
farther  side  as  1.01816  to  unity.  The  difference  in  the  terms  of  the  ratio  in  the 
latter  case  is  twice  their  difference  in  the  former. 

It  is  worthy  of  note,  however,  that  in  the  process  of  the  lengthening  of  the 


THE    MOON.  407 

or  parts  free  to  move  would,  therefore,  be  determined  by 
terrestrial  gravity.  This  fact  renders  undemonstrable  the 
conclusion  that  water  and  air  are  absent  from  the  moon, 
since  the  opposite  side  might  be  covered  by  a  sea  432  feet 
deep*  in  the  middle  without  reaching  to  the  visible  hemi- 
sphere; and  a  corresponding  atmosphere  might  rest  upon 
its  surface.  But  the  complete  absence  of  all  refraction, 
and  all  spectroscopic  change  in  the  stellar  or  solar  light 
passing  close  to  the  limb  of  the  moon,  tends  to  negative 
the  supposition  of  water  or  air,  since  if  they  existed  on 
the  remoter  hemisphere,  air  and  aqueous  vapor  would 
occasionally  reveal  themselves  upon  the  moon's  limb,  espe- 
cially at  times  when  the  lunar  librations  enable  us  to  see 
beyond  the  limits  of  the  mean  hither  hemisphere.  It  is, 
therefore,  eminently  safe  to  conclude,  as  we  have,  that  the 
water  and  air  of  the  moon  have  completely  disappeared.! 

lunar  revolution  there  was  an  epoch  when  the  moon's  distance  was  such  that 
differential  centrifugal  force  was  just  equal  to  differential  attraction  exerted  by 
the  earth.  This,  according  to  my  calculation,  was  when  the  moon's  angular 
velocity  was  1.398  times  its  present  angular  velocity,  which  implies  a  period  of 
19  days,  12  hours,  59  minutes  and  29  seconds.  At  this  epoch  the  fluids  would 
have  tended  to  distribute  themselves  equally  around  the  satellite  in  spite  of 
synchronistic  motions.  At  a  remoter  epoch,  with  a  still  shorter  revolution,  the 
fluids  would  have  tended  to  accumulate  on  the  perigoal  side. 

*  Were  the  earth  non-rotating  (as  the  moon  is  practically)  and  covered  by  a 
fluid,  its  tidal  semi-axis  would  exceed  its  shorter  semi-axis  58  inches,  under  the 
moon's  influence.  Hence  if  the  moon's  apogeal  hemisphere  were  covered  with 
water,  it  would  be  maintained,  making  no  allowance  for  tidal  yielding  of  the 
moon's  body  at  a  depth  approximately  of  38%  inches  X  134-432  feet.  This, 
strictly,  is  the  height  to  which  the  geal  tide  would  rise  if  the  moon  were  cov- 
ered with  water  and  the  moon's  body  were  a  rigid  sphere. 

It  may  be  interesting  to  note  that  if  the  moon  possesses  no  surface  water, 
and  its  bodily  rigidity  is  such  that.under  geal  tid.il  influence  it  yields  one-half  as 
much  as  a  watery  envelope  would,  then  the  protuberance  at  each  extremity 
of  tha  prolate  axis  is  432  X  V\  =  216  feet. 

tThe  foregoing  views  respecting  the  tidal  evolution  of  the  moon  were  writ- 
ten out  substantially  as  here  given  in  March,  1S81.  I  had  not  then  seen  or  heard 
of  M.  Faye's  memoir  on  the  geology  of  the  moon,  in  the  Annualre  for  1881,  in 
which  somewhat  similar  conceptions  are  set  forth,  and  from  which  some  cita- 
tions are  made  in  the  present  exposition  of  my  views.  M.  Faye,  however,  denies 
the  former  presence  of  water  or  air  on  the  moon,  and  denies  all  analogy  between 
the  ancient  activity  of  the  moon  and  terrestrial  volcanoes. 

According  to  the  general  theory  here  set  forth,  the  crater  phenomena  of  the 


408  SPECIAL   PLANETOLOGY. 

It  would  seem  that  lunar  synchronous  motions  were 
attained  while  yet  molten  matter  remained  in  the  interior. 
The  crater  floors  present  the  appearance  of  solidified  lava 
pools.  They  conform  to  the  general  curvature  of  the 
moon's  surface.  But  the  thousands  of  feet  to  which  we 
find  these  floors  sunken,  must  bear  a  small  ratio  to  the 
whole  thickness  which  the  crust  had  attained  at  the  epoch 
of  synchronism.  Were  the  upper  layer  of  the  molten 
matter  at  any  stage  of  the  same  density  as  the  crust,  the 
fluid  would  rise,  in  the  case  of  a  moon  no  longer  tidally 
disturbed,  to  the  general  level  of  the  lunar  surface.  If 
the  fluid  were  lighter  than  the  crust  it  would  rise  above 
this  level;  if  it  were  heavier,  it  would  come  short  of  it. 
But  the  fluid  was  heavier  than  the  crust,  or  the  crust 
would  have  sunken.  The  depth  of  the  lunar  crater,  there- 
fore, is  determined  by  the  excess  of  density  of  the  molten 
matter  over  the  density  of  the  superincumbent  crust. 
When  we  reflect  that  this  excess  was  very  slight,  we  can 
easily  understand  that  a  crater-bottom  sunken  10,000  feet 
implies  a  total  thickness  for  the  crust  many  times  as  great. 

After  the  close  of  those  tidal  actions  which  wrought 
out  the  grand  features  of  the  moon's  surface,  there  re- 
mained some  concluding  results  of  the  long  course  of  pro- 
gressive refrigeration.  First,  the  subsequent  lowering  of 
the  general  temperature  of  the  crust  increased  its  density, 
and  consequently  its  pressure  on  the  subjacent  fluid;  the 
fluid  as  a  consequence,  sought  to  rise  through  opening's  in 
the  crust,  or  to  burst  through  the  weaker  places  of  the  crust. 
There  were  few  places  so  weak  or  so  recently  consolidated 
as  the  crater  floors;  and  in  these  the  thinnest  and  the  least 

moon  ought  to  be  the  most  numerous  in  the  region  near  the  plane  of  the  lunar 
orbit;  but  maps  of  the  moon  show  them  continuing  with  scarcely  diminished 
frequency,  quite  to  the  vicinity  of  the  selenographic  poles. 

Further,  on  lunar  craters,  the  reader  may  consult  M.  Bergeron,  La  Nature, 
1882,  copied  in  Pop.  Sd.  Monthly,  xxii,  495-7.  illus.,  Feb.,  1883;  also  H.  J.  Klein, 
Petermann's  Mittheilungen,  translation  in  Observatory,  and  reproduced  in  Kan- 
tat  City  Review,  vi,  467,  Dec.  1882. 


THE    MOON.  409 

supported  parts  were  the  central  portions.  Here,  then,  the 
residual  fluid  might  most  easily  press  through.  Secondly, 
the  same  reduction  of  temperature  resulted  in  contraction 
of  the  crust;  and  from  this  cause  it  pressed  with  increas- 
ing pressure  upon  the  subjacent  fluid.  There  was  indeed, 
a  time  when  the  volume  of  that  fluid  was  relatively  large 
and  its  own  abatement  of  temperature  more  than  compen- 
sated for  the  increased  constriction  resulting  from  crustal 
contraction.  But  when  the  volume  of  fluid  was  greatly 
reduced  and  its  protected  situation  caused  much  slower 
loss  of  heat,  it  seems  probable  that  increase  of  crustal 
pressure  would  impel  portions  of  the  included  fluid  to 
seek  chances  of  escape.  Thirdly,  the  progressive  thick- 
ening of  the  crust  implies  that  liquid  portions  of  lunar 
matter  were  continually  becoming  solid  portions;  that  is, 
that  some  of  the  matter  beneath  the  crust  was  becoming 
expanded  and  demanding  more  space.  The  action  of  these 
freshly  solidifying  portions  upon  the  contiguous  fluid 
furnished  another  source  of  pressure  which  made  it  neces- 
sary to  seek  relief.  In  these  three  causes,  it  seems  to  me, 
we  have  an  explanation  of  those  late  exudations  of  lava 
which  might  have  produced  the  central  masses  resting 
upon  the  floors  of  nearly  all  the  lunar  craters.*  These  have 

*  Since  this  was  written  I  have  read  for  the  first  time  some  remarks  by  Mr. 
W.  Mattiea  Williams,  presented  to  the  Royal  Astronomical  Society,  March, 
1873,  in  a  paper  on  The  Origin  of  Lunar  Volcanoes.  He  refers  to  the  cooling  of 
"tap  cinder"  from  puddling  furnaces,  which  is  received  in  stout  iron  boxes  or 
"cinder  bogies."  "If  a  bogie  filled  with  fused  cinder  is  left  undisturbed,  a 
veritable  spontaneous  volcanic  eruption  takes  place  through  some  portion,  gen- 
erally near  the  centre,  of  the  solid  crust.  In  some  cases  this  eruption  is  suffi- 
ciently violent  to  eject  small  spurts  of  molten  cinder  to  a  height  equal  to  four 
or  five  diameters  of  the  whole  mass.  The  crust  once  broken,  a  regular  crater  is 
rapidly  formed,  and  miniature  streams  of  lava  continue  to  pour  from  it;  some- 
times slowly  and  regularly,  occasionally  with  jerks  and  spurts  due  to  the  burst- 
ing of  bubbles  of  gas.  The  accumulation  of  these  lava  streams  forms  a  regular 
cone  the  height  of  which  goes  on  increasing.'1  The  circumstances  under  which 
these  miniature  cones  are  formed  seem  to  be  extremely  analogous  to  those  of 
the  old  crater  holes  on  the  moon  after  the  attainment  of  the  crustal  quiescence 
due  to  the  establishment  of  synchronistic  motions. 


410  SPECIAL   PLANETOLOGY. 

been  broken  and  dismembered  by  the  movements  attending 
the  final  stage  of  complete  solidification  of  the  satellite, 
as  such  final  movements  may  also  have  fractured  the  cra- 
ter rims  and  opened  the  thousand  rifts  in  the  general  sur- 
face. They  have  also  been  subjected  to  whatever  erosive 
action  may  result  from  the  extreme  fluctuations  of  tem- 
perature supposed  to  be  experienced  on  the  lunar  surface. 

These  central  monticles  were  therefore  post-synchronis- 
tic, and  the  result  of  the  last  stages  of  lunar  refrigeration. 
Since  that  epoch  was  reached,  tidal  and  thermal  forces 
being  extinct,  the  lunar  surface  has  presented  only  an 
unchanging  scene  of  mighty  desolations,  oppressive  still- 
ness and  dead  stagnation. 

5.  The,  Atmospheric  Factor  in  Lunar  History. —  On 
the  ground  of  nebular  theory,  the  moon  in  segregating 
from  the  earth,  whether  through  annulation  or  rupture, 
must  have  received  a  portion  of  atmosphere  or  the  ele- 
ments of  such  an  envelope.  As  to  the  relative  amount  of 
atmosphere,  we  can  scarcely  make  any  other  assumption 
than  that  its  mass  bore  nearly  the  same  ratio  to  the  earth's 
present  atmosphere  as  the  moon's  mass  bears  to  the  earth's. 
The  mass  of  the  lunar  atmosphere  would  be  one  factor  in 
the  determination  of  its  relative  pressure  on  the  lunar 
surface.  The  amount  of  surface  on  which  it  presses  would 
be  another  factor.  As  the  moon's  surface  is  greater  in 
comparison  with  the  earth's  than  the  moon's  mass  in  com- 
parison with  the  earth's,  this  difference  would  diminish 
the  relative  pressure  on  each  unit  of  lunar  surface.  The 
earth's  mass  is  80  times  the  moon's,  but  its  surface  is  only 
13£  times  the  moon's.  Aside  from  difference  in  atmos- 
pheric masses,  pressure  would  be  inversely  as  the  areas  of 
the  moon  and  earth;  or  what  is  the  same  thing,  inversely 
as  the  squares  of  the  radii  of  the  two  bodies.  Again, 
with  equal  atmospheric  masses  and  equal  planetary  sur- 
faces, the  relative  intensity  of  gravity  would  be  another 


THE    MOON.  411 

factor  in  determining  the  atmospheric  pressure  on  a  planet. 
When,  therefore,  we  multiply  together  the  ratio  of  the 
masses  of  the  moon  and  earth,  the  inverse  ratio  of  their 
surfaces  and  the  ratio  of  the  intensities  of  gravity  on  the 
two  bodies,  we  find  the  relative  atmospheric  pressure  to  be 
.02787  at  the  time  when  its  normal  proportion  of  the 
atmospheric  medium  was  still  present.*  This  result  is 
somewhat  surprising,  and  leads  to  interesting  inferences. 
The  barometric  column  stood  at  .836  of  an  inch,  which 
implies  an  atmospheric  pressure  too  insignificant  to  con- 
stitute a  positive  factor  in  a  planet's  genetic  development; 
though  it  implies  the  virtual  absence  of  those  terrestrial 
actions  which  depend  on  the  terrestrial  atmosphere,  and 
thus  enables  us  to  trace  the  divergence  between  the  his- 
tories of  the  two  bodies. 

A  barometric  column  of  five-sixths  of  an  inch  corre- 
sponds to  a  terrestrial  altitude  of  17.7  miles,  or  over  three 
times  the  height  of  the  Himalayas.!  Under  such  a  pres- 

*  We  may  embody  these  principles  in  a  ger.eral  formula.  If  M,  S,  R,  g  and 
P  represent  the  mass,  surface,  mean  radius,  gravitational  intensity  and  atmos- 
pheric pressure  of  the  earth ;  and  »t,  s,  r,  g'  and  p,  the  same  constants  for  any 
other  planet,  then 

m     S     g'_        m     R2     g>  _        R     £     £ 
'    M  '  s  '  g  ~  r  '  M  '    r3  '  g  ~     '   r  '  p  '  g 
where  p  and  p'  represent  planetary  densities  respectively. 

In  the  case  of  the  moon  ^  =  .0125,  -=  13.471  and  ~=  .1655. 
And  p  =  .02787  P. 

If  we  take  the  mean  height  of  the  mercurial  column  as  the  measure  of  P, 
then  the  normal  mean  height  of  the  barometer  on  the  moon  must  have  been 
h  =  30  inches  X  .02787  =  .836  inch. 

t  The  formula  for  the  barometric  calculation  of  heights  in  the  latitude  of 
Great  Britain  is 

h  =  log  -  x  [60360  +  (6  —  32°)  (122.68)]  (Maxwell :  Tlieory  of  Heat,  222;  see 
also,  Deschanel:  Natural  Philosophy,  Everett's  ed.,  164),  where  P  and  p  are 
the  pressures  at  the  upper  and  lower  stations,  and  h  is  the  height  in  feet  for  a 
temperature  t  on  Fahrenheit's  scale.  Here  we  may  assume  the  temperature  at 
32°  Fahr.  Hence  the  second  term  in  the  second  factor  reduces  to  zero  and  we 

haVe  *=  log  JX  60360. 

In  the  present  case  P  -  30  inches  and  p  =  .836;  hence 
h  =  93.854.669  ft.  •-=  17.77  miles. 


412  SPECIAL   PLAtfETOLOGY. 

sure  the  boiling  point  of  water  would  be  at  37^°  Fahr.*  —  a 
result  of  extreme  interest.  The  first  inference  to  be  de- 
duced from  this  atmospheric  tenuity  is  the  comparatively 
advanced  stage  of  cooling  attained  before  the  precipita- 
tion of  water  began.  The  second  is  the  very  limited 
duration  of  the  period  of  sedimentation,  which  would, 
indeed,  be  further  slightly  shortened  by  the  commence- 
ment of  ice-formation  at  a  temperature  above  32°.  f 

The  third  inference  is  the  low  altitude  at  which  the 
clouds  must  have  been  borne  in  so  thin  an  atmosphere, 
since  only  the  lightest  cirrus  clouds  are  borne  by  the  ter- 
restrial atmosphere  at  an  altitude  of  about  eight  miles,  or 
one-half  that  required  for  the  tenuity  of  the  lunar  atmos- 
phere. In  short,  it  may  even  be  doubted  whether  vapor 
would  be  formed  on  the  moon,  even  close  to  its  surface, 
of  sufficient  density  to  cause  rain.  Not  unlikely,  the  only 
precipitation  was  a  cold  fog  resting  on  the  surface  of  the 
planet.  In  this  view,  there  was  no  erosion  by  waters,  and 
no  sedimentation;  and  the  moon's  water  was  absorbed 
simultaneously  with  the  air.  With  a  little  further  cooling 
of  the  planet,  the  lunar  solidifying  temperature  of  water 
was  reached;  and  thereafter  it  was  revealed  in  the  liquid 
state  only  in  situations  when  the  sun's  direct  rays  caused 
some  elevation  of  temperature  above  the  mean.  A  fourth 
inference  from  the  existence  of  an  atmosphere  of  such 
extreme  tenuity,  and  holding  so  little  vapor,  concerns  the 
influence  of  the  sun's  radiations  on  the  lunar  surface.  It 
is  well  understood  that  the  atmospheric  and  vaporous 

*By  Soret's  formula  (Deschanel:  Nat.  Phil.,  Everett's  ed.,  338), 

h  =  538  (212°  —  <), 

where  t  =  the  temperature  on  Fahrenheit's  scale  at  which  water  boils  at  the 
height  h  in  feet.  Whence 


In  the  present  case  h  =  93,854.669  ft.,  .-.  t  =  37'/2°  Fahr. 

tSee  Maxwell:   Theory  of  Heat,  176-7,  and  the  authorities  there  cited.    See 
also,  this  work,  pp.  270-2. 


THE    MOON.  413 

envelope  of  the  earth  absorbs  a  large  percentage  of  the 
sun's  thermal  radiations,  and  partially  restrains,  also,  the 
escape  from  the  earth  of  such  heat  as  succeeds  in  reaching 
it.  The  lunar  condition  here  considered,  therefore,  admit- 
ted a  higher  intensity  of  solar  heat,  but  at  the  same  time, 
all  situations  with  free  radiation  sent  the  heat  back  with 
correspondingly  increased  rapidity.  The  situation  is  ap- 
proached when  we  ascend  to  the  summit  of  a  very  high 
mountain.  The  sun's  rays  are,  indeed,  hotter,  but  the 
terrestrial  radiation  is  augmented  in  still  greater  ratio, 
and  the  temperature  is  lower.  Rising  through  the  atmos- 
phere we  remove  successively  some  of  the  protective 
wrappings  which  keep  the  earth  warm.  Professor  S.  P. 
Langley  has  reported  some  observations  made  on  the 
summit  of  Mount  Whitney,  a  peak  of  the  Sierra  Nevada 
in  southern  California,  attaining  an  altitude  of  13,000 
feet.  Here  the  solar  rays  heated  to  the  boiling  point 
some  water  in  a  copper  kettle  covered  with  two  pieces  of 
window  glass  to  prevent  radiation.*  From  these  and 
other  observations,  it  appears  that  our  atmosphere  at  sea 
level  absorbs  about  one-half  of  all  the  radiant  solar  energy 
—  luminous,  thermal  and  actinic — and  that  the  selection 
of  rays  to  undergo  absorption  is  such  that  the  white  light 
reaching  us,  formed  of  the  united  rays  of  certain  wave 
lengths,  is  not  the  color  of  the  light  resulting  from  the 
complete  union  of  all  the  solar  rays,  but  contains  far  too 
little  of  the  blue  and  violet  rays.  Hence,  Professor  Lang- 
ley  concludes,  the  color  of  the  sun  seen  from  a  point 
beyond  our  atmosphere  would  be  not  only  bluish,  but 
positively  blue.  This,  we  must  conclude,  therefore,  is  the 

*  S.  P.  Langley:  The  Mt.  Whitney  Expedition,  Nature,  xxvi,  314-7.  Further, 
on  the  "  selective  absorption"  of  the  atmosphere,  see  his  paper  before  the  Brit- 
ish Association,  1882,  in  Jfature,  xxvi,  586-9,  Oct.  12,  1882,  republished  in  Amer. 
Jour.  Sci.,  Ill,  xxiv,  393-8;  also  a  memoir  in  Amer.  Jour.  ScL,  III,  xxv,  169-%, 
March,  1883.  Detailed  results  of  the  Mt.  Whitney  Expedition  are  to  be  published 
by  the  "U.  S.  Signal  Service." 


414  SPECIAL  PLANETOLOGY. 

color  of  the  sun  mewed  from  the  moon,  either  after  the 
complete  absorption  of  its  atmosphere,  or  even  while 
retaining  its  normal  atmosphere  in  such  a  state  of  tenuitv 
as  has  been  indicated.  In  open  space  the  rapidity  of  radi- 
ation, according  to  Professor  Langley,  must  be  so  great 
that  in  spite  of  the  intensity  of  the  sun's  rays,  a  sus- 
pended body  would  sink  to  a  temperature  below  — 50° 
Fahr.  This,  then,  from  this  point  of  view,  must  be  the 
upper  limit  of  the  surface  temperature  of  the  sunny  side 
of  the  moon;  and  thus  the  fluctuations  of  temperature 
during  a  lunation  must  be  vastly  less  than  Lord  Rosse  and 
others  have  calculated;  and  the  modern  changes  due  to 
thermal  fluctuations  are  diminished  correspondingly.  Dur- 
ing the  whole  lunar  lifetime,  even  while  the  normal 
amount  of  atmosphere  remained  on  the  moon's  surface, 
the  temperature,  after  the  formation  of  a  cold  crust,  must 
have  remained  nearly  at  —50°  Fahr.  or  below.*  Not  only 
water,  therefore,  but  mercury  and  other  substances  known 
to  us  as  liquids  or  gases,  existed  on  the  moon  only  as 
solids.  In  this  view,  the  conception  of  aqueous  erosion 
and  sedimentation  is  entirely  excluded,  save  so  far  as  the 
primitive  inherent  heat  of  the  satellite  maintained  at  the 
surface  a  liquefying  temperature.  At  the  time  when  the 
residual  effect  of  solar  radiation,  inherent  heat  and  lunar 
radiation  produced  a  surface  temperature,  say  between 
34°  and  37°  Fahr.,  water  may  have  rested  on  the  lunar 
surface  during  the  lunar  day,  but  it  would  be  consolidated 
during  the  lunar  night.  As  some  of  this  water  occupied 
the  pores  of  the  rocks,  here  was  a  cause  of  considerable 
disintegration,  so  long  as  the  water  had  not  sunken  be- 
yond the  reach  of  the  thermal  fluctuations.  In  any  view, 

"This  statement  must  be  modified  so  far  as  the  retention  of  the  moon's 
water  in  the  atmosphere  would  increase  absorptive  effects  experienced  by  the 
sun's  rays.  The  ratio  of  aqueous  vapor  to  the  whole  atmosphere  was  much 
greater  than  the  ratio  of  aqueous  vapor  in  the  terrestrial  atmosphere,  and  rose  to 
the  ratio  existing  on  our  planet  before  primeval  precipitation  began. 


MAES.  415 

however,  there  seems  little  ground  for  inferring  that  the 
process  of  sedimentation  was  an  important  factor  in  any 
stage  of  lunar  development. 

Thus,  an  attentive  consideration  of  the  divergences 
between  lunar  and  terrestrial  conditions  reveals  the  inter- 
esting fact  that  lunar  history  must  have  presented  charac- 
teristics widely  divergent  from  those  of  terrestrial  history; 
and  in  this  divergence,  the  tenuity  of  the  moon's  atmos- 
phere has  performed  a  part  quite  comparable  with  the 
energetic  work  of  the  tides. 

§3.  MARS. 

1.  Phenomena  of  Mars  and  their  Interpretation. — 
This  planet  has,  in  relation  to  the  earth,  a  surface  of 
.2828,  a  volume  of  .1470,  a  mass  of  .1108,  a  density  of 
.7537  and  an  intensity  of  gravity  at  the  surface  of  .3917. 
Its  lower  density  may  reasonably  be  attributed  to  its 
smaller  mass.  The  length  of  planetary  periods  on  Mars 
would  be,  according  to  the  method  of  calculation  pre- 
viously employed,*  about  two-fifths  as  great  as  on  the 
earth.  Hence,  if  the  earth's  incrustation  began  fourteen 
million  years  ago,  Mars  reached  the  earth's  present  condi- 
tion in  less  than  five  and  a  half  million  years  after  incrus- 
tation began.  If  Mars  and  the  earth  began  incrustation 
at  the  same  epoch,  Mars  had  reached  its  habitable  stage 
nine  and  a  half  million  years  ago,  or  at  the  beginning  of 
Eozoic  Time.  This  expresses  the  relative  rates  of  evolu- 
tion of  the  two  planets  independently  of  any  assumed  nu- 

««-!-fit— »-dk; 

It  will  be  noticed  that,  as  in  the  case  of  the  moon,  the  same  number  expresses 
the  relative  length  of  the  planetary  period,  and  relative  gravity  at  the  planet's 
surface.  This  is  because  relative  gravity  varies  as  the  mass  and  inversely  as 
the  square  of  the  radius,  and  the  relative  length  of  the  planetary  periods 
varies  as  the  mass  and  inversely  as  the  surface;  that  is,  as  the  mass  and 
inversely  as  the  square  of  the  radius.  These  calculations  take  no  account  of 
centrifugal  force  on  the  several  planets. 


416  SPECIAL   PLANETOLOGY. 

merical  value  of  the  earth's  age,  if  we  accept  the  table  of 
time  ratios  previously  given. 

According  to  our  theory,  Mars  is  an  older  planet  than 
the  earth;  and  for  this  reason,  as  well  as  its  more  rapid 
rate  of  senescence,  it  should  be  much  further  advanced  in 
planetary  life  than  the  earth.  The  stage  of  atmospheric 
absorption,  however,  if  we  adopt  the  popular  view,  seems 
not  yet  to  have  been  attained;  and  astronomers  used  to 
speak  confidently  of  extensive  watery  areas  on  the  surface. 
Moreover,  we  witness  polar  phenomena  which  seem  to  in- 
dicate alternate  advance  and  retreat  of  the  polar  ice  caps. 
On  the  whole  the  physical  phenomena  have  been  under- 
stood to  indicate  a  planetary  stage  not  very  different  from 
that  attained  by  the  earth.  But  we  may  doubt,  not  alone 
on  theoretical  grounds,  but  from  the  admitted  fallacy  of 
similar  opinions  formerly  entertained  concerning  the 
moon,  whether  the  diversified  shades  of  color  seen  on  Mars 
imply  the  real  existence  of  surface  water.  An  inspection 
of  a  map  of  Mars  shows  a  distribution  of  light  and  dark 
shades  which  is  very  improbable,  viewing  them  as  areas  of 
land  and  water.  There  are  too  many  and  too  extensive 
long  and  slender  arms  of  the  sea,  and  these  do  not  show 
any  conformity  to  any  fundamental  planetary  cause.  The 
longer  axes  tend  rather  to  be  transverse  to  the  meridians 
than  coincident  with  them.  If  the  white  areas  about  the 
poles  are  really  snow-covered  surfaces,  as  Sir  William  Her- 
schel  first  suggested,  it  might  be  inferred  that  the  climates 
are  quite  comparable  to  those  of  the  earth.  The  greater 
inclination  of  the  planetary  axis  to  the  orbit,  by  the 
amount  of  5°,  would  tend  to  diminish  the  extent  of  both 
polar  ice  caps.*  Although  the  alternate  advance  and  re- 
treat of  these  white  areas,  with  the  changes  in  the  seasons, 
is  confirmatory  of  the  prevalent  opinion  respecting  their 
natures,  this  must  still  be  regarded  a  question  under  con- 

*PartII,ch.ii,§9,3. 


MARS.  417 

sideration.  The  ruddy  color  of  Mars  is  generally  ascribed 
to  a  dense  atmosphere;  but  surely,  if  such  an  atmosphere 
existed,  clouds  of  aqueous  vapor  must  sometimes  obscure 
some  portions  of  the  disc,  and  sometimes,  indeed,  the 
whole  of  it.  In  fact,  the  existence  of  polar  snow  implies 
the  existence  of  clouds.  These  have  never  been  noted, 
even  in  the  polar  regions  of  the  planet.  Father  Secchi 
attributes  a  thin  atmosphere  to  Mars  and  states  that  white 
spots  are  occasionally  seen  on  his  disc,  which  may  be 
regarded  as  clouds,  and  that  whirlwind  movements  may 
sometimes  be  seen  in  them.*  But  these  statements  in 
view  of  the  results  of  calculations  here  adduced  may  well 
be  distrusted.  There  is  much  reason,  therefore,  to  doubt 
whether  the  popular  interpretation  of  the  visible  phe- 
nomena of  Mars  is  the  correct  one.f 

2.  Tidal  and  Atmospheric  Influences  on  Mars. — The 
tidal  efficiency  of  the  sun  on  the  surface  of  Mars  is  .4306 
relative  to  his  tidal  efficiency  at  the  distance  of  the  earth. 
The  whole  vertical  fluctuation  of  the  solar  tide,  therefore, 
on  the  surface  of  the  water-covered  planet  would  be  four- 
teen inches,  assuming  that  the  conditions  are  otherwise 
such  as  enable  the  moon  to  cause  upon  the  earth  a  tidal 
fluctuation  of  fifty-eight  inches.  J  The  tidal  influence  of 

*  Secchi:  Le  Soleil,  ii,  392. 

tProf.  Elias  Loomis,  nearly  thirty  years  ago,  advanced  the  opinion  that  the 
equatorial  region  of  Mars  must  have  a  mean  temperature  at  11°  Fahr.  below 
zero,  and  the  poles,  51°  below  zero,  and  raises  the  question  how  the  Martial 
snow  caps  could  ever  diminish  under  such  temperatures.  (Loomis,  Proc. 
Amer.  Assoc.,  1855,  74-80.) 

t  Employing  the  notation  used  when  treating  of  the  moon  (p.  384),  and 
denoting  by  /  the  sun's  tidal  efficiency  at  the  earth  and  by  /'  its  efficiency  at  a 
different  distance,  the  general  formula  becomes 

M    /'     r    £ 
'  m  •  f  •  R  '  tf 
But  the  tide-producing  body  being  the  same  in  the  two  cases  here  compared, 

^  =  1.    Also,  here,  j-  =  .4306,  ~  =  ^7  and  ^  =  f£f  J,  whence  t  =  .6122  T; 

and  when  T  =  58  X  |  =  23.2  inches, 

t  =  23.2  X  .6122  =  14.2  inches. 
27 


418  SPECIAL   PLANETOLOGY. 

the  earth  upon  Mars  is  entirely  insignificant,  not  amount- 
ing, at  the  perigee  of  Mars,  to  a  total  fluctuation  of  more 
than  one  four-hundredth  of  an  inch.  The  satellites  of 
Mars,  though  in  proximity  sufficiently  close  to  acquire 
marked  tidal  efficiency,  possess  too  little  mass  to  exert 
any  important  influence.  The  inner  satellite,  Phobos,  if 
having  a  diameter  of  twenty-five  miles,  a  distance  of  6,000 
miles  from  the  centre  of  its  primary,  and  a  density  equal 
to  that  of  the  primary  (which  is  probably  too  great), 
would  cause  upon  the  ocean-covered  surface  of  the  planet 
a  total  linear  tidal  fluctuation  of  only  ten  and  a  quarter 
inches  according  to  my  calculation.*  The  evolution  of 

*It  will  be  best,  with  a  view  to  future  applications,  to  deduce  a  rough  gen- 
eral formula  for  the  linear  value  of  the  tidal  fluctuation  on  any  tide-bearer,  pro- 
duced by  any  tide-mover. 

1.  Symbols  referring  to  tide-bearer. 

Let  T  =  fluctuation  of  tide  on  the  earth  produced  by  its  tide-mover, 
D  —  distance  of  the  earth's  tide-mover, 
R  =  radius  of  the  earth, 
M  =  mass  of  the  earth, 

g  =  intensity  of  gravity  on  the  earth. 

t  —  fluctuation  of  tide  on  any  other  tide-bearer, 

d  =  distance  of  the  other  tide-bearer  from  its  tide-mover, 

r  =  radius  of  the  other  tide-bearer,   • 
m  —  mass  of  the  other  tide-bearer, 

g'=  intensity  of  gravity  on  this  tide-bearer. 

2.  Symbols  referring  to  tide-mover. 
m'=  mass  of  tide-mover  acting  on  the  earth, 

/a.  =;  mass  of  the  other  tide-mover. 

'-'•5-H-^-i- 

T)s 
where    — ^  =  tidal  efficiency  depending  on  distance, 

—r  =  effect  depending  on  mass  of  tide-mover, 
—  =  effect  depending  on  radius  of  tide-bearer, 
~  =  effect  depending  on  Intensity  of  gravity. 

But          g'=g.'£.  ~,  and  by  substitution, 

.  D3     n    M     M 

~-*'~'-'- 


MARS.  419 

Mars,  therefore,  has  proceeded  without  any  considerable 
interposition  of  tidal  forces. 

Supposing1,  as  I  have  done  in  the  case  of  the  moon, 
that  the  Martial  atmosphere  bore  the  same  ratio  to  the 
mass  of  the  planet  as  the  earth's  atmosphere  to  the  earth's 
mass,  the  density  of  the  planet's  atmosphere  would  be 
.138  relative  to  the  earth's  atmospheric  pressure.  This 
corresponds  to  a  barometric  altitude  of  4.14  inches.* 
Hence  the  atmospheric  pressure  on  Mars  would  be  only 
such  as  our  atmosphere  possesses  at  an  altitude  of  9.83 
miles  above  sea  level.  f  This  result  discloses  at  once  a 
wide  contrast  between  the  surface  condition  of  Mars  and 
that  of  the  earth,  even  during  the  period  while  Mars 
retained  its  normal  amount  of  atmosphere.  The  thermal 
effect  of  the  sun's  rays  would  be  greatly  diminished;  and, 
when  we  reflect  that  the  sun's  mean  intensity  at  the  dis- 
tance of  Mars  is  less  than  half  that  at  the  earth,  it  be- 
comes apparent  that  the  temperature  at  all  seasons  must 
be  considerably  below  that  of  the  earth.  With  the  atmos- 
pheric pressure  so  low,  we  find  that  water  would  boil  at 
the  temperature  of  about  115°  Fahr4  Hence  precipita- 

This  formula  is  identical  with  that  deduced  from  the  general  expression  for 
a  tide  (p.  229).  but  the  rationale  is  here  made  more  intelligible. 

In  the  present  case,  if  we  make  comparison  with  the  fluctuation  of  the  lunar 


tide  on  the  earth,  T  =  58  inches;        =  =  64000:  ~  =  (.5503)3;        a 


1         u.          (25)3    x  .700 


(6000)3    -         w'  R3 


.1081'  m'       (2160)3  X  .607' 

And  t  ^  10.24  inches. 

*  Using  the  formula  given  in  the  discussion  on  the  moon,  we  have 
m  S       (3963)2  tf 


Whence  p  -  .138  P. 
If  we  take  the  measure  of  P  as  the  mean  height  of  the  mercurial  barometer, 

p  =  30  in.  X  .138  =  4.14  inches. 
t  Using,  as  before,  the  formula  for  barometric  measurement  of  altitudes, 


4.14 
JFrom  Soret's  formula,  as  before, 


-"«"  =  lir.5F.hr. 


420  SPECIAL    PLANETOLOGY. 

tion  and  sedimentation  did  not  begin  on  this  planet  until 
cooling  had  advanced  a  hundred  degrees  further  than  on 
the  earth.  As  solidification  of  water,  under  diminished 
atmospheric  pressure,  took  place  at  a  slightly  higher  tem- 
perature than  on  the  earth,  the  range  of  temperature 
within  which  denudation  and  sedimentation  could  have 
been  carried  on  was  greatly  contracted.  The  attenuated 
atmosphere  also  promoted  escape  of  heat  from  the  planet. 
These  considerations  all  point  to  a  more  rapid  attainment 
to  successive  planetary  stages,  and  lead  definitely  to  the 
conclusion,  indicated  on  other  grounds,  that  Mars  is  not 
lingering  in  the  terrestrial  stage,  but  has  lost  all  water 
and  atmosphere,  and  advanced  far  toward  the  lunar  stage 
of  total  refrigeration. 

§  4.   VEXUS  AND  MERCURY. 

1.  Venus. — Next  to  Mars,  Venus  is  generally  supposed 
to  sustain  closest  planetary  relations  to  the  earth.  Its 
diameter  is  .9475;  its  volume,  .855;  mass,  .875;  density, 
1.03,  and  the  intensity  of  gravity  at  the  surface,  .982,  the 
earth's  corresponding  values  being  unity.  The  relative 
intensity  of  solar  radiations  at  Venus  is  1.913,  or  nearly 
twice  that  at  the  earth's  distance.  The  relative  length 
of  the  planetogenetic  periods,  according  to  principles 
previously  explained,  is  .977.  Solar  tidal  efficiency  is 
2.643,  and  the  relative  linear  height  of  the  solar  tide  is 
2.543,  which,  on  a  water-covered  planet,  implies  a  total 
fluctuation  of  7.37  feet.  The  pressure  of  the  atmosphere, 
calculated  from  ratio  of  mass  and  surface,  is  .9595,  which 
corresponds  to  a  mean  barometric  height  of  29.78  inches,  an 
elevation  on  the  earth  of  192.91  feet  above  sea  level,  and 
a  boiling  point  of  211°.64  Fahr.  In  every  particular,  there- 
fore, Venus  reproduces  nearly  the  conditions  of  the  earth, 
except  those  which  arise  from  greater  proximity  to  the 


VEXUS    AND    MEEOUKY.  421 

sun  —  intensity  of  heat,  light  and  tidal  action,  and  these 
are  not  very  widely  different.  We  may  therefore  suppose 
a  planetary  history  not  far  divergent  from  that  of  the 
earth.  The  surface  of  Venus  is  stated  by  some  observers 
to  b<3  densely  veiled  in  clouds. 

The  nebular  theory  implies  an  increasing  density  toward 
the  centre  of  the  nebula,  not  only  in  consequence  of  in- 
ternal pressure,  but  probably  through  the  gravitation  of 
the  denser  constituents  of  the  nebular  mass  toward  the 
centre.  The  first  cause  would  not  operate  after  the  sepa- 
ration of  the  planetary  mass.  Density  due  to  superincum- 
bent pressure  would  now  depend  on  the  radius  of  the 
planet  and  the  coefficient  of  condensation  of  the  material 
under  pressure.  As  Venus  has  a  shorter  radius  and  higher 
density,  there  is  manifestly  a  certain  amount  of  density 
due  to  the  fact  that  the  proportion  of  denser  materials  is 
somewhat  greater  in  Venus  than  in  the  earth,*  and  this  is 
as  it  should  be.  This  subject,  however,  is  connected  with 
what  follows. 

The  excess  of  solar  heat  upon  Venus  must  have  exerted 
some  influence  upon  the  evolution  of  the  planet.  The 
rate  of  cooling  was  somewhat  impeded,  and  this  effect  was 
relatively  greatest  in  the  later  and  cooler  stages.  After 
the  epoch  of  aqueous  precipitation,  the  solar  heat  efficiently 
reinforced  the  inherent  heat  of  the  planet  in  promoting 
copious  evaporation  and  cloud  formation.  When  the  in- 
herent heat  had  so  diminished  that  its  surface  influence 
became  similar  to  that  of  the  earth  in  historic  times,  the 
excessive  heat  of  the  sun  still  maintained  a  copiousness  of 
evaporation  double  that  upon  the  earth.  As  long  as  this 
rate  of  evaporation  could  be  maintained,  there  must  have 

*  If  the  condensation  of  solids  were  proportional  to  pressure,  as  in  gases, 
the  density  in  this  case  would  be  .9519,  and  the  excess  of  the  actual  density  would 
be  .078.  But  the  condensation  in  solids  is  in  a  lower  ratio  than  the  pressure,  and 
this  excess  is  too  great. 


422  SPECIAL   PLANETOLOGY. 

been  also,  a  double  amount  of  precipitation.  But  the 
effect  reacted  on  the  cause.  The  clouds  formed  prevented 
the  free  access  of  heat  to  the  planet,  and  the  amount  of 
cloud  formation  and  consequent  precipitation  was  propor- 
tionally diminished.  The  final  adjustment  of  these  causes 
and  effects  determined  a  ratio  of  cloudiness  and  precipita- 
tion much  greater  than  on  the  earth,  but  somewhat  less 
than  twice  as  great.  Meantime  the  cloudy  envelope  of 
the  planet  must  be  nearly  complete  and  permanent,  I 
know  of  no  groiind  for  negativing  the  assumption  that  the 
vaporous  veil  which  protects  Venus  is  of  such  density  as 
to  admit  about  the  same  amount  of  heat  and  light  as  is 
received  by  the  earth.  The  conditions  on  the  planet's  sur- 
face may  easily  be  analogous  to  those  upon  the  earth  on  a 
thinly  clouded  day.  But  while  the  cloudy  envelope  screens 
out  solar  heat  to  the  terrestrial  standard,  it  restrains,  also, 
the  process  of  radiation  from  the  planet.  Consequently 
the  depression  of  temperature  during  the  night  is  relatively 
less.  Further,  supposing  the  axis  inclined  toward  the 
plane  of  the  orbit,  seasonal  periods  mark  the  year.  But, 
in  the  winter  season,  the  diminution  of  the  sun's  intensity 
simply  clears  the  atmosphere  to  a  corresponding  extent. 
The  winter  season  is  therefore  the  season  of  clearest  skies. 
If  Venus  is  surrounded  by  a  perpetual  mantle  of  clouds, 
astronomers  have  never  seen  the  body  of  the  planet.  Its 
diameter  is  therefore  less  and  its  density  greater  than  have 
been  calculated;  and  we  have  so  far  confirmation  of  our 
deductive  conclusion  that  Venus  possesses  a  greater  pro- 
portion than  the  earth  of  the  heavier  substances  of  the 
primeval  nebula.  In  this  view  also,  the  diameter  of  the 
planet  is  not  accessible  to  measurement;  and  the  deter- 
mination of  the  rotary  period  will  not  be  accomplished. 
There  might  be  produced  a  belted  arrangement  of  lighter 
and  darker  clouds  in  the  equatorial  region;  but  no  fixed 


VEXUS   AND    MERCURY.  423 

feature  is  likely  to  afford  the  means  of  ascertaining  the 
length  of  the  day.* 

2.  JHercury. —  Passing  to  Mercury,  we  find  a  planet 
whose  relative  diameter  is  .3858;  surface,  .1489;  volume, 
.0574;  mass,  .065;  density,  1.12;  solar  intensity  at  peri- 
helion, 10.58;  at  aphelion,  4.59,  with  a  mean  of  7.58.f 
Its  relative  intensity  of  gravity  is  .432,  which  is  only  equal 
to  that  exerted  by  the  earth  at  the  elevation  of  2,066 
miles  above  its  surface.  The  relative  length  of  the  plane- 
tary periods,  is  therefore,  .4366;  mean  solar  tidal  efficiency 
is  17.24,  and  the  mean  linear  fluctuation  of  the  solar  tide 
in  an  oceanic  envelope  would  be  15.41  or  29.79  feet.  At 
perihelion  the  solar  tidal  efficiency  is  34.39,  and  the  rela- 
tive linear  fluctuation  in  an  oceanic  envelope  is  31.71, 
which  implies  an  actual  fluctuation  of  66.49  feet.  This 
tidal  influence  is  experienced  every  88  days.  The  tidal  in- 
fluence of  Venus,  when  nearest  Mercury,  compared  with 
the  lunar  tide  on  the  earth,  would  be  only  .000068,  or 
about  four  thousandths  of  an  inch.  The  pressure  of  the 
atmosphere  should  be  .1882,  corresponding  to  a  barometric 
height  of  5.646  inches. J  This  pressure  is  attained  on 
the  earth  at  an  elevation  of  8.29  miles,  and  implies  a  boil- 
ing point  for  water  of  130°. 8  Fahr.  As  Mercury's  per- 
centage of  atmosphere  is  probably  less  than  the  earth's,^ 
the  results  just  given  are  probably  too  large.  Mercury, 
therefore,  differs  from  the  earth  to  a  very  marked  extent, 
not  only  in  those  points  connected  with  greater  nearness 

*  Cassini,  guided  by  certain  supposed  spots,  calculated  the  rotation  period  as 
a  little  less  than  twenty- four  hours.  Schroter,  by  observations  along  the  "ter- 
minator," believed  that  he  had  fixed  the  period  of  rotation  at  .973  d.  This 
method  implies  the  existence  of  high  mountains  on  the  planet. 

tThe  orbit  of  Mercury  has  an  eccentricity  thirty  times  that  of  Venus  and 
twelve  times  that  of  the  earth. 

J  Mr.  W.  Mattieu  Williams  makes  it  four  and  one-fourth  inches,  but  his  method 
of  calculation  is  not  indicated.— Current  Discussions  in  Science,  Ilumboldt 
Library,  No.  41,  p.  20. 

§  Mercury  has  sometimes  been  represented  by  observers  as  covered  by  a 
dense  atmosphere  loaded  with  clouds. 


424  SPECIAL   PLANETOLOGY. 

to  the  sun,  but  also  in  everything  connected  with  smaller 
mass. 

We  have  here  a  further  and  much  more  decisive  exem- 
plification of  the  theoretical  principle  that  heavier  matter 
accumulated  about  the  centre  of  the  primitive  nebula, 
since,  while  Mercury's  diameter  is  only  three-eighths  as 
great  as  the  earth's,  its  density  is  nine-eighths  as  great. 
Aside  from  the  influence  of  solar  heat  in  retarding  Mer- 
cury's developmental  progress,  we  might  probably  regard 
this  planet  as  advanced  to  a  habitable  stage. 

In  consequence  of  the  powerful  tidal  action  exerted, 
Mercury  must  have  undergone  an  incrustive  history  some- 
what analogous  to  that  of  the  moon,  but  very  much  less 
violent.  Aside  from  any  consideration  of  the  presence  of 
water,  it  seems  likely  that  its  surface  was  powerfully 
marked  by  crater  formations  and  an  extensive  system  of 
fractures.  But  water  was  present,  though  probably  in 
less  proportion  than  on  the  earth,  and  some  erosion  and 
sedimentation  have  taken  place,  if  we  can  admit  the  solar 
heat  moderate  enough  to  allow  aqueous  precipitation. 
During  the  day,  with  the  solar  intensity  from  4£  to  10£ 
times  that  experienced  by  us,  it  is  scarcely  credible  that 
rain  should  fall  except  in  situations  protected  by  vapors. 
These  would  exist  even  during  the  day,  and  most  copi- 
ously in  the  perihelion  period;  for  in  spite  of  the  sun's 
intensity  upon  the  exposed  surface  of  the  clouds,  the 
rapidity  of  radiation  would  probably  preserve  a  tempera- 
ture low  enough  for  condensation.  During  the  night, 
however,  condensation  would  be  vastly  more  copious,  and 
hence  the  night  side  of  the  planet  would  be  deeply  veiled, 
and  also  deluged  with  rain.  A  violent  thunder  storm  fol- 
lowed sunset  around  the  planet  continually.  Thus  all  sides 
of  the  planet  were  enveloped  in  cloudy  vapors,  hovering, 
however,  close  to  the  surface.  This  condition  of  things 
began  when  the  inherent  heat  had  sufficiently  abated  to 


JUPITER.  425 

permit  a  temperature  of  131°.  I  know  of  no  advanced 
condition  ^nvhich  should  prevent  its  continuance  to  the 
present  epoch.  The  powerful  tidal  action  experienced  by 
Mercury  has  greatly  retarded  its  primitive  axial  motion, 
and  increased  its  distance  from  the  sun.  No  surprise 
would  be  occasioned  by  the  proof  that  the  planet  has 
already  attained  to  synchronistic  motions.  Its  retirement 
from  the  sun  has  been  accompanied  by  a  growing  infre- 
quency  of  perihelion  positions  and  a  diminishing  intensity 
of  all  the  solar  influences. 

Mercury,  therefore,  as  well  as  Venus,  is  screened  from 
telescopic  observation,  and  nothing  can  be  known  of  its 
actual  diameter  or  period  of  rotation.*  Owing,  however, 
to  the  thinness  of  its  atmosphere,  and  the  low  altitude  of 
the  clouds,  the  real  density  of  the  planet  cannot  be  much 
greater  than  has  been  calculated. 

§5.   JUPITER. 

1.  Physical  Relations. — This  planet,  in  consequence  of 
its  enormous  mass,  presents  physical  conditions  immensely 
different  from  those  of  the  earth.  Compared  with  the 
earth,  Jupiter  has  a  diameter  of  11.06;  a  surface  of  117.9; 
a  volume  of  1279.412;  a  mass  of  308.990;  a  density  of 
.242;  a  force  of  gravity  at  the  equator,  making  allowance 
for  centrifugal  effect,  of  2.254.f  As  the  rotation  period 
is  9  hours  55  minutes  and  34  seconds,  the  equatorial  cen- 
trifugal force  is  63.13  times  as  great  as  on  the  earth,  and 

*  Schriiter's  observation,  giving  a  day  of  twenty-four  hours,  five  minutes,  has 
not  been  confirmed  by  other  astronomers  using  far  superior  instrnmenta, 

t These  data  are  taken  from  the  Annuaire  du  Bureau  des  Longitudes,  1881. 
They  differ  somewhat  from  those  given  in  the  Encyclopedia  Britannica  ;  and 
both  differ  somewhat  from  Newcomb's  tables  in  his  Popular  Astronomy.  It 
will  be  found  that  the  results  of  calculations  in  this  chapter  are  in  some  cases 
inharmonious  with  each  other,  in  consequence  of  employing  data  in  different 
cases  from  different  authorities. 


426  SPECIAL   PLANETOLOGY. 

diminishes  materially  the  effective  force  of  gravity.*  Dis- 
regarding the  effects  of  rotation,  the  relative  surface 
gravity  of  Jupiter  is  2.619.f  This  is  therefore  the  force 
of  gravity  at  the  poles,  neglecting  the  effect  of  oblateness. 
In  any  other  latitude  the  actual  intensity  of  gravity  is 
given  by  diminishing  the  stationary  gravity  by  the  vertical 
component  of  the  centrifugal  force  in  that  latitude.  The 
centrifugal  force  at  the  earth's  equator  is  equivalent  to 
0.1112  feet  per  second, \  and  that  on  the  equator  of  Jupiter 

*  Letting  r,  f,  t  and  v  represent  the  mean  radius,  equatorial  centrifugal  force, 
rotation  period  and  equatorial  velocity  of  Jupiter,  and  R,  F,  T  and  V  the  same 

y-2 

IF 

and/  =  ^-2.     Therefore  F  :/::R^  :  J2and  /  =  F^  •  R.    .But  v  :  V  ::  ?  :   ~  .-. 

^  =  15  '  R^  '  and'  8ub8tituting>  /  =  F '  7?  =  ^-  Bv  Pitting  T  =  86,164  seconds, 
t  =  35,720  seconds,  It  =  3959  miles,  r  =  43,000  miles  and  F=  1,  we  obtain/  =  63.13. 
The  vertical  component  of  the  centrifugal  force  in  any  latitude  A,  is  therefore 
/'=  63.13  cos-'  A,  and  for  the  latitude  of  45°,/'  =  31.57. 

t  Since  surface  gravity  is  directly  as  the  mass  and  inversely  as  the  square  of 

the  radius,  we  have,  adopting  notation  similar  to  the  last,  g'  =  g  ^  •  —^  =  2.619. 

Taking  the  oblateness  of  Jupiter  as  --35'  and  the  mean  diameter  as  84,843 
lu.oo 

(Encyc.  Brit.),  equatorial  gravity  is  reduced  to  .9601  of  the  gravity  computed  on 
the  assumption  of  a  spherical  planet,  This  reduces  the  force  of  gravity  on 
Jupiter's  equator  to  2.619  X  .9601  =  2.515.  For,  if  D  and  d  represent  the  trans- 
verse and  conjugate  diameters  of  the  oblnte  spheroid,  and  r,  the  radius  of  the 
equivalent  sphere, 

f  -n  rs  =  \n  D2  d;  whence  D2  x  8>'3. 
d 

But,  as  —    —  =  rHw'  ^  =  i~?rV  an(^  ^''^'tuting, 

D3  =  8.504  r3,  and  D  =  2.041  r  =  86,590  miles; 
|r- ,  =  81,460,  and  D  —  d  =  5130  miles. 

Finally,  if  g'  and  g"  represent  equatorial  gravity  on  the  sphere  and  spheroid, 


%  The  equations  F  =  ~  and-  V=      ~-  give  ns  F  = 

Whence,  taking  the  mean  radius  of  the  earth  at  20,923,900  feet,  according  to  Sir 
John  Herschel,  F  =  .1112  feet  per  second.  Whence  the  equatorial  centrifugal 
force  on  Jupiter  is  .1112  X  63.13  =  7.085.  Or,  we  may  obtain  this  result  from  the 
independent  formula, 


whence  d  =  ,08  **    .  =  81,460,  and  D  —  d  =  5130  miles. 


JUPITER.  427 

is  63.13  times  as  much,  or  7.02  feet.  As  the  space  through 
which  a  body  falls  in  a  given  time  is  proportional  to 
gravity,  a  body  falling  16.1567  feet  in  one  second  on  the 
earth's  equator,  making  no  allowance  for  centrifugal  force, 
or  16.0455  under  the  actual  centrifugal  force,  would  fall, 
on  Jupiter's  equator,  42.3  feet,  making  no  allowance  for 
centrifugal  force,  or  35.3  feet  under  the  actual  centrifugal 
force  on  that  planet. 

When  we  attempt  to  reach  some  conception  of  the 
relative  length  of  planetary  periods  on  Jupiter,  it  becomes 
apparent  that  the  great  present  disparity  of  densities 
renders  it  necessary  to  reduce  Jupiter  to  the  earth's  den- 
sity, or  to  reduce  the  earth  to  Jupiter's  density.  Now,  if 
Jupiter  had  the  density  of  the  earth,  his  mean  diameter 
would  be  53,530  miles;*  his  relative  surface,  45.7,  and  the 
relative  length  of  his  geological  periods,  6.761  times  the 
length  of  the  corresponding  periods  on  the  earth. f  If,  on 
the  contrary,  the  earth  were  reduced  to  the  density  of 
Jupiter,  its  diameter  would  be  12,721  miles  and  its  surface 
jtg-  that  of  Jupiter,  or  2.581  times  its  present  surface.]; 

*  Employing  notation  as  bef  ore.  ^  =  ^,  densities  being  the  same.     Hence 

„,       .'/m  K3          * '308J99  X  13959;*'     ,„  _„.      ., 
r    ~\T~=    T    ~  7^ —  =  26, 76o  miles. 

+  Employing  the  same  principle  as  heretofore, 


£  Since  on  this  supposition  ~r  —  =^—i 
M       K  -J 


R'  =  V^H-  //I  X  (43000)3  _ 
Further,  the  earth's  relative  surface  011  this  supposition  would  be 

|~-=  .02198, 


and  since  ^^  =  45.7,  this  number  represents  Jupiter's  surface  relatively  to  the 
earth  when  reduced  to  Jupiter's  density. 

c  • 

Also,  S'=  -- 

times  the  earth's  present  surface. 


AISO,  s-  ^  = l  xjy  =  2  _M1 


428  SPECIAL   PLANETOLOGY. 

In  this  case  the  surface  of  Jupiter,  in  relation  to  that  of 
the  earth,  would  be  45.7.  as  before,  and  the  relative  dura- 
tion of  his  planetary  periods  would  be  6.761,  as  before.* 
But  basing  a  calculation  on  Jupiter's  actual  volume,  as 
ordinarily  stated,  we  find  the  relative  length  of  his  planet- 
ary periods  to  be  2.62.  Some  idea  of  the  relative  energy 
of  meteorological  forces  on  this  planet  may  be  had  by 
recalling  the  fact  that  the  velocity  of  the  trades  and  anti- 
trades is  determined  by  the  velocity  of  a  point  on  the 
planet's  equator.  In  Jupiter,  we  have  a  planet  rotating 
2.4  times  as  rapidly  as  the  earth,  with  a  radius  11  times 
as  great.  Hence,  a  point  on  his  equator  moves  more  than 
26  times  as  rapidly  as  a  point  on  the  terrestrial  equator; 
and  other  things  being  the  same,  the  Jovian  trades  and 
anti-trades  should  move  with  a  terrific  velocity.  Their 
effects,  moreover,  would  be  increased  six-fold  by  the  supe- 
rior density  of  Jupiter's  atmosphere.  But  other  things 
are  not  the  same,  since  the  solar  heat  at  the  distance  of 

*  Jupiter's  actual  surface  in  relation  to  the  earth's  actual  surface  is  117.9. 
The  earth's  surface,  if  having  the  density  of  Jupiter,  would  be,  in  relation  to  the 
present  surface,  2.5S1:  and  hence  Jupiter's  actual  surface  in  relation  to  the 


when  Jupiter  is  supposed  reduced  to  the  earth's  density.    It  may  be  readily 

shown  that  this  is  as  it  should  be,  for, 

Let  S  and  «  represent  the  surfaces  of  the  earth  and  Jupiter, 

S'  and  s'  their  surfaces  respectively,  when  each  is  reduced  to  the  other's 

density, 
R  and  r  their  actual  radii,  and  R'  and  r'  their  radii  respectively,  when  re- 

duced each  to  the  other's  density; 
Then,          .,'=S.g  =  gwhenS  =  l;  and,  =  8.1  +  8.^  =  ^. 

Now,  if  a-  and  <r'  represent  Jupiter's  two  supposed  densities,  and  p  and  p'  the 
earth's,  and  v,  »',  V  and  V  be  employed  similarly  for  volumes  of  Jupiter  and  the 
earth,  we  have 


y 

„'  =  p  =  i,  and  f/  =  tr; .:  r*i  =  rt  pf  I,  and  R'2   =  -51. 


Hence,  by  substituting         «'  =     f'l,  and  «  =  — gp 


JUPITER.  429 

Jupiter  is  only  ^  the  intensity  experienced  at  the  earth  — 
taking  no  account  of  the  warming  influence  of  the  supe- 
rior density  of  the  atmosphere.  As  solar  heat  is  the 
cause  of  the  atmospheric  circulation,  it  appears  that  the 
velocity  of  the  Jovian  trades  must  be  about  the  same  as 
that  of  the  terrestrial  trades,  if  the  Jovian  atmosphere  is 
of  the  same  depth.  But  the  solar  thermal  disturbance  of 
equilibrium  being  less,  the  velocity  of  the  movement  due 
to  this  is  less:  the  velocity  to  and  from  the  equator  is  less 
rapid,  and  for  this  reason,  combined  with  the  superior 
rotary  velocity  of  the  planet,  the  resultant  movement 
across  the  meridians  approaches  much  more  nearly  a  right 
angle.  The  Jovian  atmosphere,  also,  as  will  presently  be 
seen,  is  probably  much  deeper,  as  it  certainly  is  much 
denser,  than  that  of  the  earth;  and  the  heat  radiated 
from  the  planet  more  than  compensates,  probably,  for 
deficiency  of  solar  heat.  Hence  it  is  fair  to  infer,  finally, 
-that  the  circulation  of  the  atmosphere  is  much  more  active 
and  powerful  upon  Jupiter  than  upon  the  earth.  Profes- 
sor Hough  reports  drifting  movements  of  white  spots  on 
his  disc  at  the  rate  of  260  miles  an  hour,  and  these  also 
in  the  direction  of  the  planet's  rotation.  This  state  of 
things  offers  an  explanation  of  the  belted  condition  of 
Jupiter's  equatorial  region.* 

2.  Jupiter's  Retarded  Development. — The  data  just 
presented  concerning-  Jupiter's  physical  condition  bring  to 
view  a  stage  of  world-life  very  remote  from  that  on  the 
earth.  The  superior  volume  of  Jupiter,  if  constituted  like 
the  earth,  should  give  it  a  density'many  times  greater  than 
the  earth,  instead  of  one-fourth  as  great.  Some  remark- 
able planetary  cause  produces  this  great  difference.  The 
visible  surface  of  the  planet  is  constituted  of  moving  and 

*  On  the  remarkable  bright  "  red  spot"  visible  on  Jupiter's  disc  in  1879-80- 
1-2,  see  Nature,  xxvi,  613,  Oct.  19,  1882,  for  a  notice  of  studies  by  Professor  G. 
W.  Hough,  at  Dearborn  Observatory,  Chicago,  from  his  Annual  Report. 


430  SPECIAL   PLANETOLOGY. 

changing  vapors,  which,  by  the  rapid  axial  rotation,  are 
drawn  into  parallel  belts,  especially  in  the  equatorial 
region.  These  appear  to  exclude  from  view,  perpetually, 
the  real  body  of  the  planet.  Moreover,  the  presumed 
relations  of  the  atmosphere  to  the  mass  and  surface  grav- 
ity of  the  planet  point  out  exceptional  conditions.  If 
the  atmosphere  on  Jupiter  sustains  the  same  relation  to 
the  planetary  mass  as  the  terrestrial  atmosphere  to  the 
earth's  mass,  it  must  be  accumulated  to  nearly  three  times 
the  terrestrial  amount  over  each  square  mile  of  surface. 
Since  Jupiter's  mass  is  309  times  the  earth's,  while  his 
surface  is  only  118  times  as  great,  this  atmosphere  would 
therefore  be  accumulated  over  each  unit  of  surface  in  2.G2 
times  as  great  quantity  as  on  the  earth,  and  would  there- 
fore, for  this  reason,  be  2.62  times  as  dense  as  the  earth's 
atmosphere.  But  as  Jupiter's  gravity  is  2£  times  as  great 
as  the  earth's,  the  actual  density  would  be  over  6  times 
as  great  as  the  earth's.*  The  Jovian  atmosphere  reduced 
to  uniform  surface  density  would  reach  an  altitude  .4123 
that  of  the  earth's  homogeneous  atmosphere;  that  is,  only 
2.075  miles,  f  All  corresponding  densities  in  Jupiter's 

*Irt  the  formula  previously  employed  (p.  411)^  =  309;    -  = -~i-:  -  = 

2.254  (Annuaire,  1881).    Hence  p  =  P  x  6.357;  and  if  P  =  30  inches,  p  =  190.71 
inches  of  mercury.    This  pressure  is  equivalent  to  that  which  would  exist  in 
the  bottom  of  u  shaft  on  the  earth  91.8  miles  deep,  and  would  raise  the  tempera- 
tn  re  of  hoiling  water  to  302°  Fahr.,  which  is  somewhat  less  than  the  txperinifnfal 
result  for  saturated  steam  under  the  same  pressure  on  our  planet 
tlf  u  =  the  volume  of  the  atmosphere  of  a'planct, 
«  =  the  surface  of  the  planet, 

m  =  mass  of  atmosphere.     (If  this  is  taken  relative  to  mass  of  earth's 
atmosphere,  then  m  =  mass  of  planet  relative  to  earth's  mass.) 
IT  =  density  of  atmosphere  at  surface  of  tin-  planet. 

then  h'  =  -  approximately. 

But  n 


For  Jupiter,  the  relative  values  of  these  constants  are  m  =  309;  s  -  117.9;  a  = 

6.357  (=  p  in  last  note);  hence  h'  =  .4143  h. 

To  get  h,  the  height  of  the  earth's  homogeneous  atmosphere,  we  have  h  =  = 


JUPITER.  431 

atmosphere  would  be  correspondingly  lower  than  in  the 
earth's.  That  is,  half  the  surface  density  would  be  reached 
at  1£  miles,  while  on  the  earth  it  is  reached  at  3|  miles. 
The  inference  is,  as  Professor  Proctor  has  shown,  that  the 
floating  clouds  of  Jupiter's  atmosphere  must  rest  in  com- 
parative proximity  to  his  surface,  instead  of  being  elevated 
to  atmospheric  heights  proportional  to  Jupiter's  volume. 
But  astronomical  observers  inform  us  of  phenomena  which 
make  it  necessary  to  admit  considerable  depth  to  the  cloud- 
layer.  The  special  black  lines  in  the  spectrum  indicate,  in 
all  the  exterior  planets,  deep  and  dense  atmospheres. 
Should  we  admit  a  depth  of  thirty  miles,  this  would  imply 
such  a  volume  of  atmosphere  as  would  condense  the  sur- 
face layers  to  fifty  times  the  density  of  platinum.  We  are 
compelled  to  assume,  therefore,  that  a  very  peculiar  plan- 
etary condition  exists  on  the  surface  of  Jupiter.  Some 
cause  is  in  action  which  at  the  same  time  greatly  reduces 
the  density  of  the  planet  and  greatly  increases  the  volume 
o'f  the  cloud-bearing  envelope. 

Now,  on  the  principles  of  the  nebular  theory,  it  is  per- 
fectly legitimate  to  assume  that  Jupiter  is  lingering  in  the 
high  thermal  stages  of  planetary  life.  Lhave  shown  that 
progress  on  his  surface  must  be  6f-  times  as  slow  as  on  the 
earth;  so  that  if  Jupiter  had  emerged  as  a  separate  body 
at  the  same  epoch  as  the  earth,  he  must  lag  far  behind  in 
development.  It  is  quite  supposable  that  though  his 
planetary  existence  may  have  begun  long  before  the 
earth's  he  may  not,  for  all  that,  be  so  far  developed,  and 

But  I"  =.003837  X  f  *  R3,  and  S  =  4  ir  R2;  therefore  h  =  .00127  R  =  5.033  miles. 
This  is  given  also  by  the  height  of  the  column  of  mercury  in  the  barometer. 

To  get  .003837,  relative  volume  of  earth's  atmosphere,  we  have 
Mass  of  atmosphere  =  TYOWTTTF  —  -000000833  (Herschel). 

Density  of  air  =  0<0     -  (Regnault). 

OlO.Ol 

Density  of  air  compared  with  earth's  density  =  — ; —  X :. 

Hence  U  =  f  IT  R3  x  5.66  X  813.67  X  .000000833  =  5  JT  R3  x  .003837. 


432  SPECIAL   PLANETOLOGY. 

may  even  have  but  recently  reached  the  stage  of  incipient 
incrustation  and  cloud  formation.  The  implied  tempera- 
ture would  retain  his  density  at  a  comparatively  low  fig- 
ure, and  would,  besides,  evolve  a  volume  of  cloud-support- 
ing gases  which  would  greatly  exaggerate  the  apparent 
diameter  of  the  planet.  I  have  shown  that  if  possessed  of 
the  density  of  the  earth,  his  diameter  would  be  53,000 
miles  instead  of  85,000,  so  that  to  present  his  present 
apparent  volume,  there  must  be  an  atmosphere  capable  of 
bearing  clouds  16,000  miles  above  his  solid  surface.  As 
no  such  atmospheric  thickness  is  admissible,  the  planetary 
body  must  actually  possess  much  less  density  than  the 
earth;  and  this  condition  can  be  most  naturally  referred 
to  heat  as  its  cause. 

The  luminosity  of  Jupiter  seems  to  confirm  this  conclu- 
sion. Experiments  made  byZ6llner*on  the  light  emis- 
sive powers  of  the  moon  and  the  planets  exterior  to  the 
earth,  after  making  all  allowances  for  difference  of  dis- 
tances and  diameters  of  the  bodies,  supply  us  with  data 
from  which  the  following  table  may  be  calculated: 

COMPARATIVE    LIGHT-EMISSIVE    PROPERTIES. 

Moon 1.000    Saturn 2.869 

Mars 1.539    Uranus 3.687 

Jupiter 3.598    Neptune 2.794 

Now,  it  is  universally  admitted  that  the  lunar  surface 
presents  the  condition  of  cooled  and  solid  rocks,  somewhat 
analogous  to  the  surface  of  the  earth.  It  is  reasonable  to 
assume  that  the  moon's  reflective  powers  are  about  as 
great  as  a  surface  of  the  lunar  or  terrestrial  character  can 
attain.  Of  what,  then,  must  the  surfaces  of  Jupiter  and 
the  remoter  planets  be  composed  to  possess  reflecting 
powers  from  2^  to  3£  times  as  great  as  the  moon?  It  is 
safe  to  deny  that  any  such  reflecting  powers  are  possessed 

ZOllner:  Grundziige  e'mer  allgemeinen  Photometric  lies  Himmels.  Berlin, 
1861. 


JUPITER.  433 

by  planetary  masses.  The  only  alternative  is  the  admis- 
sion that  Jupiter  and  his  giant  companions  possess  still 
some  amount  of  inherent  luminosity,  or  are  wrapped 
in  envelopes  possessing  higher  reflecting  powers  than 
solid  planetary  materials. 

The  rapid  rotation  of  Jupiter  is  evidence  that  tidal 
action,  presently  to  be  mentioned,  has  not  gone  far  in 
destroying  its  rotary  velocity.  The  younger  and  smaller 
planets  have  suffered  much  ft  this  respect.  Rapid  rota- 
tion, according  to  our  theory,  is  a  characteristic  of  early 
periods  of  planetary  history;  and  we  here  discover  con- 
firmatory evidence  of  Jupiter's  primitive  stage  of  evolution. 

The  most  careful  scientific  examination  of  the  physical 
condition  of  Jupiter's  surface  seems,  therefore,  to  reveal 
the  actual  existence  of  a  state  of  affairs  supposed  to  have 
been  long  passed  in  the  evolution  of  our  own  planet.  The 
stormy  stage  of  Jupiter  is  a  fact  before  our  eyes,  while  the 
stormy  stage  of  the  earth  has  been  reproduced  to  thought 
only  by  a  process  of  retrograde  deduction.  It  would  be 
vain  to  attempt  to  depict  the  precise  nature  of  the  events 
taking  place  on  this  gigantic  mass,  working  out  its  plane- 
tary development  in  the  solitudes  of  boundless  space.  If 
the  planetary  body  shines  with  all  the  brilliancy  of  a 
molten  globe,  his  light  is  screened  by  a  dense  veil  of 
aqueous  vapors.  Were  Jupiter's  mass  no  greater  than  the 
earth's,  we  might  not,  perhaps,  expect  the  condensation  of 
aqueous  vapor  at  so  early  a  stage  of  cooling;  but  as  I  have 
shown,  on  a  planet  of  such  mass,  the  temperature  of  vapor 
formation  would  be  as  high  as  302°  Fahr.  Whatever  the 
condition  of  the  planetary  body,  it  is  incandescent,  and 
the  gathered  clouds  are  thick  and  dense  enough  to  pre- 
cipitate their  rains.  Into  what  a  furnace  of  consuming- 
heat  are  the  rains  falling  !  Now,  while  we  write,  that 
stupendous  and  violent  circulation  of  descending  waters 
and  ascending  vapors  which  we  have  conceived  as  a  ter- 
28 


434  SPECIAL   PLANETOLOGY. 

restrial  scene  long  past,  is  in  progress  on  an  actual  planet. 
The  lightnings  are  darting  and  the  detonations  of  the 
responsive  thunders  are  resounding,  and  the  noise  is  mag- 
nified by  the  six-fold  density  of  the  medium  which  trans- 
mits it.  To  the  naked  eye,  how  mildly  does  Jupiter 
beam  upon  our  earth  !  What  profound  stillness  reigns 
in  the  regions  of  the  sky  where  his  majesty  rides  !  Can 
we  gaze  upon  that  silent,  placid  orb  and  imagine  that  the 
elements  there  are  rending  each  other  in  very  madness, 
and  the  roar  of  their  clashing  would  stun  the  most  insen- 
sible ears  ?  We  have  good  grounds,  however,  to  picture 
the  home-life  of  Jupiter  in  the  most  startling  colors. 

Not  long  since,  cosmologically  speaking,  Jupiter  was 
shining  with  cloudless  self-luminosity.  He  was  still  a  real 
sun  revolving  about  our  great  common  centre.  There  are 
regions  in  space  from  which  our  sun  shines  like  a  fixed 
star.  From  Sirius  he  appears  as  a  star  of  a  low  order  of 
magnitude.  When  the  astronomers  in  those  regions  scan- 
ned our  star  some  millions  of  years  ago,  they  catalogued 
it  as  a  double  star.  It  had  an  attendant  which  revolved 
about  the  principal  star  in  periods  a  little  less  than  twelve 
of  our  years.  So  Alvan  Clark,  from  our  terrestrial  stand- 
point, has  detected  a  self-luminous  planet  revolving  about 
Sirius.  This  is  the  Jupiter  of  the  Sirian  system.  But  its 
period  is  fifty  years,  or  about  four  times  that  of  our  Jupi- 
ter. Thus  we  may  contemplate  Jupiter  as  marking  dis- 
tinctly one  of  the  necessary  phases  of  a  cooling  cosmical 
globe. 

3.  Tidal  Action  on  Jupiter. — Jupiter's  evolution  must 
be  perceptibly  influenced  by  the  tidal  action  of  his  satel- 
lites. The  distances  and  masses  of  these  satellites  in  re- 
lation to  their  primary  are  given  in  astronomical  tables, 
and  from  these  I  have  calculated  their  distances  in  rela- 
tion to  our  moon's  distance  from  the  earth,  and  their 
masses  in  relation  to  our  moon,  and  also  the  vertical  flue- 


JUPITER.  435 

tuations  they  are  capable  of  producing  on  the  water-covered 
planet.*     The  following  table  gives  the  results: 

Masses             Densities  Distances  Tidal  Effects 

Satellites.          (Moon's  -  1)  (Moon's  =  .607)  (Moon's  =  1)  (Inches) 

1 424               ,2009                1.084  88.21 

II 5835              .3890               1.725  33.07 

III 2.222                .3377               2.754  2813 

IV 1.067                .2618               4.842  2.49 

The  calculation  was  necessarily  based  on  a  planetary 
diameter  as  large  as  given  in  the  tables.  The  result  illus- 
trates the  predominant  importance  of  distance  in  tidal 
actions,  since  the  second  satellite,  with  more  than  a  third 
more  mass  than  the  first,  but  with  two-thirds  greater  dis- 
tance, has  only  three-eighths  as  great  tidal  efficiency.  The 
first  satellite,  also,  with  only  two-fifths  the  mass  of  our 
moon,  and  20,000  miles  more  distant  from  the  centre  of  its 
primary,  exerts  one  and  a  half  times  the  amount  of  tidal 
efficiency.  This  results  from  the  fact  that  Jupiter's  diam- 
eter is  more  than  eleven  times  that  of  the  earth. 

It  will  be  recalled  that  considerable  importance  has  been 
attached  to  lunar  action  in  the  history  of  the  earth,  even 
since  the  attainment  of  an  advanced  stage  of  incrustation. 
A  Jovian  satellite  possessing  fifty  per  cent  greater  efficiencv 
can  not  be  overlooked  as  a  working  factor  in  Jovian  evo- 
lution. The  joint  action  of  the  first  and  second  satellites 
is  more  than  double  our  moon's  influence;  and  the  joint 
action  of  the  three  nearest  satellites  amounts  to  two  and  a 
half  times  our  moon's  influence  on  the  earth,  or  a  total 
fluctuation  of  12^  feet.  Concurrences,  or  approximate 
concurrences,  of  tidal  action  very  frequently  happen. 

But  the  most  important  consideration  in  connection 
with  the  passing  history  of  the  planet,  is  the  aeriform 

*  Employing  the  same  formula  as  previously,  we  have,  for  the  first  satellite. 


D2  _  (240000)3  _  (12)3      j^  _  .000016877X300.  r  _  ff  _  _1 

7/3  ~  (260000)3  ~  (13)3   '  ~m'~          .0123          '  R~     "       '  g'  ~  2A1 
=  88.21  inches.    The  calculation  is  similar  for  the  other  satellite!?. 


436  SPECIAL    PLANETOLOGY. 

state  of  the  tide-moved  ocean  which  conceals  the  body  of 
Jupiter  from  our  view.  This  yields  with  many  times  the 
facility  of  water,  and  the  linear  extent  of  the  tidal  deform- 
ation is  correspondingly  greater.  If  we  could  assume  the 
aeriform  envelope  of  Jupiter  to  be  of  the  nature  of  pure 
air,  which  is  813.67  times  as  light  as  water,  we  should 
have,  by  dividing  this  number  by  2.425,  the  relative  inten- 
sity of  gravity  on  Jupiter's  surface,  the  actual  density  of 
the  fluid  subjected  to  tidal  fluctuation.  This  density 
would  be  335  times  less  than  that  of  water,  and  would  be 
moved,  very  approximately,  to  335  times  the  extent.  In 
other  words,  the  first  satellite  must  produce  a  fluctuation 
of  2462  feet;  the  second,  one  of  925  feet;  the  third,  one 
of  784  feet,  and  the  fourth,  one  of  70  feet.  The  concur- 
rent action  of  the  first  two  must  produce  a  difference 
of  6774  feet  in  the  two  diameters  of  the  planet;  and  the 
concurrent  action  of  the  first  three  would  cause  a  differ- 
ence of  8342  feet,  or  more  than  a  mile  and  a  half,  in  the 
flood-tide  and  ebb-tide  diameters  of  the  planet,  and  thus 
contribute  something  to  the  marked  ellipticity  which  it 
reveals. 

Solar  tidal  action  on  Jupiter  is  so  diminished  as  to 
produce  a  total  fluctuation  of  only  one  and  •one-fifth 
inches  if  the  planet  were  water-covered.  Still,  this  is 
equivalent  to  a  fluctuation  of  33^  feet  in  the  aeriform 
envelope;  and  this  amount  of  disturbance  must  be  added 
to  that  caused  by  the  satellites. 

The  retardative  influence  of  the  Jovian  tides  seems  to 
be  now  in  the  period  of  its  highest  efficiency.  Jupiter, 
like  any  other  planet  in  a  state  of  rapid  rotation,  suffers 
the  influence  of  a  correspondingly  large  lagging  angle  in 
the  tide;  and  this  augments  the  efficiency  of  the  retarda- 
tive component  of  the  tidal  force.  But,  while  Jupiter  or 
any  other  planet  exposes  an  aeriform  envelope  to  be 
acted  on,  the  free  mobility  of  its  parts  presents,  so  far  as 


JUPITER.  437 

its  movements  are  concerned,  a  compensation  for  rota- 
tional velocity.  When,  however,  any  large  part  of  the 
planet  exists  as  a  liquid  or  as  a  viscous  solid,  a  high 
rate  of  rotation  must  develop  a  large  angle  of  lagging 
and  a  large  retardative  factor.  A  planet,  therefore,  like 
Jupiter,  as  we  understand  it,  cloud-covered  above  and 
semi-liquid  within,  though  still  for  the  time  being  in  an 
early  formative  stage,  exists  at  the  same  time,  under 
those  conditions  of  high  rotation  and  semi-liquidity  which 
tend  to  degrade  most  rapidly  its  rotational  velocity.  A 
relatively  brief  epoch,  however,  in  the  history  of  a  planet 
having  309  times  the  mass  of  the  earth,  is  numerically 
long  in  the  history  of  the  earth.  Hence  it  is,  as  before 
suggested  in  reference  to  the  dissipation  of  a  planet's 
thermal  energy,  that  a  planet  older  than  the  earth  in  years 
is  so  much  younger  in  development. 

So  far,  moreover,  as  rate  of  evolution  depends  on  tidal 
retardation,  a  planet  of  large  mass  is  more  slowly  influ- 
enced than  one  of  smaller  mass,  by  a  given  tidal  efficiency. 
The  horizontal  component  of  the  tidal  force  has  indeed  the 
advantage  of  acting  at  the  extremity  of  a  longer  radius, 
but  this  advantage  is  only  proportional  to  the  first  power 
of  the  radius.  The  resistance  to  it,  for  a  given  velocity,  is 
proportional  to  the  moment  of  inertia,  or  about  the  fifth 
power  of  the  radius.*  These  relations  tend  very  greatly 

*  The  moment  of  inertia  of  a  sphere  is  measured  by  the  mass  into  the  radius 
of  gyration,  or,  in  common  language,  =  M  /fc*.  Among  spheres  of  the  same  den- 
sity, and  having  uniform  internal  density \  moment  of  inertia  —  .4.  ir  r3  X  t  ra  = 
1.6758  r6.  That  is,  resistances  to  action  of  horizontal  component  of  attraction 
on  tidal  protuberance  are  measured  by  1.6758  times  the  fifth  power  of  the  ra- 
dius; but  they  are  supposed  applied  at  the  extremity  of  the  radius  of  gyration, 
which  is  equal  to  .6325?'.  A  unit  of  force  applied  here  is  equivalent  to  .5811 
applied  at  the  extremity  of  the  radius.  Hence  the  moment  of  inertia  of  the 
sphere,  supposed  applied  at  the  extremity  of  the  radius,  where  the  retardative 
force  is  applied  (very  approximately),  becomes  1.6758r6  X  .5811  =  .9736r5.  That 
is,  the  effective  resistance  of  the  moment  of  inertia  is  as  the  fifth  power  of 
the  radius. 


438  SPECIAL   PL  A  FETOLOGY. 

to  a  relative  prolongation  of  evolution  stages  in  the  larger 
planets. 

4.  Tidal  Effects  and  Densities  on  Jupiter's  Satellites. — 
I  have  heretofore  pointed  out  the  remarkable  tidal  influ- 
ence exerted  by  the  earth  on  the  moon,  and  it  is  proper  to 
consider  what  part  has  been  performed  by  the  tidal  influ- 
ence of  Jupiter  in  the  evolution  of  his  satellites.  Two 
circumstances  point  at  once  to  the  certainty  that  the  tidal 
action  exerted  by  Jupiter  must  be  enormous.  His  mass  is 
309  times  that  of  the  earth,  and  25,122  times  that  of  our 
moon,  and  hence,  other  things  being  the  same,  the  lunar 
tide  on  the  earth  must  be  multiplied  by  this  number  to 
show  the  magnitude  of  the  Jovian  tide  on  one  of  his  satel- 
lites. Secondly,  the  satellites  all  possess  a  lower  inten- 
sity of  gravity  than  the  earth,  and  for  this  reason,  with  a 
given  diameter  they  present  less  resistance  to  the  tide-rais- 
ing efforts  of  the  planet. 

If  we  consider  the  case  of  the  first  satellite,  and  sup- 
pose, for  the  sake  of  comparison,  that  an  ocean  covers  its 
surface,  it  will  be  evident  first,  that  so  far  as  mass  of  the 
tide-mover  enters  into  the  calculation,  it  is  25,122  times 
that  of  the  tide-mover  in  the  case  of  lunar  tides  on  the 
earth.  Secondly,  so  far  as  concerns  the  effect  of  distance, 
it  will  be  as  the  cube  of  12  to  the  cube  of  13,  which 
is  .7865.  Thirdly,  assuming,  as  heretofore,  that  the 
linear  altitude  of  the  tide  is  proportional  to  the  radius 
of  the  tide-bearer,  the  value  of  this  factor  will  be  as  the 
radius  of  the  satellite  to  the  radius  of  the  earth  —  that  is, 
as  1176  to  3963  which  is  .2967.  Fourthly,  the  relative 
intensities  of  gravity  on  the  satellite  and  on  the  earth  will 
constitute  another  factor,  and  the  height  of  the  tide  will 
be  inversely  proportional  to  the  two  intensities.  These  a 
little  calculation  shows  to  be  as  .05922  to  unity,  the  recip- 
rocal of  which  is  16.89.  The  product  of  these  four  factors 
shows  that  the  Jovian  tide  on  the  first  satellite  is  99,000 


JUPITER.  439 

times  as  great  as  the  lunar  tide  on  the  earth.  If  we  de- 
sire to  express  this  in  some  comprehensible  measure,  we 
may  assume,  as  heretofore,  that  the  tidal  linear  fluctuation 
of  the  lunar  tide  is  58  inches;  and  from  this  it  will  result 
that  the  tidal  effect  of  Jupiter  on  his  first  satellite  is  equiva- 
lent to  an  oceanic  fluctuation  of  more  than  90  miles.* 
This  amazing  result  indicates  a  degree  of  prolateness  in 
this  satellite  which  possibly  might  be  detected  by  the  best 
measurements;  though  90  miles,  at  the  distance  of  Jupi- 
ter, subtends  an  angle  of  only  one  twenty-fifth  of  a  second. 
That  is  to  sayj  if  the  satellite,  while  making  a  transit 
across  the  planet's  disc,  has  an  angular  diameter  of  1".02, 
it  should  have  at  its  elongations  a  horizontal  diameter  of 
1".06. 

To  the  tidal  effect  must  be  added  the  tidal  effects  of 
any  other  satellites  when  in  conjunction  with  the  first  one. 
A  little  calculation  shows  that  the  tidal  effect  of  the 
second  on  the  first,  when  in  conjunction,  is  over  fifty-three 
feet  of  water. f 

With  this  disclosure  of  the  tidal  distortion  of  the 
Jovian  satellites,  we  can  appreciate  the  certainty  of  their 
rapid  approach  to  a  state  of  synchronistic  rotation.  If 
this  state  was  not  attained  before  the  disappearance  of 
the  water  belonging  to  one  of  them,  the  tidal  oscillations 
must  have  acted  with  most  destructive  energy  upon  the 

*  We  may  adapt  the  formula  heretofore  used,  and  abbreviate  the  operation 
as  follows :  In  the  expression 

,  _T     D3     r_s     M     ^ 
da  '  R3  '  m  '  m 

d  =  distance  of  first  satellite  from  Jupiter, 
/•  =  radius  of  the  same,  and  m  =  its  mass, 
H  =  the  mass  of  Jupiter. 

1     .  1 


(13)6       (3963)3  ~  .0123       .000016877 
miles. 

+  Applying  still  the  general  formula, 

(280)3       (1176)3  1  .000023227 

(154)3  X  (3963)3  X  .000016877  .0123 


=  5,743,000  inches  =   90.64 


440  SPECIAL    PLANETOLOGY. 

solid  crust.  The  tidal  movements  of  the  crust  itself 
developed  constant  fissures  through  which  the  molten  inte- 
rior escaped  in  enormous  ejections,  and  the  planetary 
waters  poured  within,  developing  explosive  energy  suffi- 
cient to  hurl  fragments  beyond  the  sphere  of  the  satellite's 
attraction.  If  the  volcanic  action  continued  after  the 
retirement  of  the  water,  as  I  have  assumed  in  the  case  of 
our  moon,  a  process  of  crater  formation  must  have  taken 
place  similar  to  that  occurring  on  the  moon,  but  as  much 
more  violent  as  the  tidal  efficiency  was  greater  on  the 
Jovian  satellite.  It  is  to  be  presumed,  therefore,  that  it 
presents  a  disc  more  fearfully  scarred  than  that  of  our 
moon.  The  enormous  irregularities  of  the  surface  present, 
in  the  course  of  a  rotation,  various  aspects  toward  the 
sun.  In  some  situations  the  exposures  are  such  as  to 
reflect  much  more  light  than  in  others;  and  hence  the 
brilliancy  of  the  satellite  varies,  as  has  been  observed. 
But,  in  this  view,  the  same  aspects  should  reappear  with 
each  return  of  the  same  exposure.  If  these  reappearances 
should  be  found  correlated  only  with  the  orbital  move- 
ments, the  fact  would  indicate  that  the  axial  rotation 
moves  synchronously  with  the  orbital  revolution.  If  it 
should  appear  that  the  recurrences  do  not  correspond 
with  orbital  positions,  it  must  be  inferred  that  synchro- 
nism does  not  exist;  and  then  the  period  of  the  recurren- 
ces might  afford  a  clew  to  the  satellite's  period  of  rota- 
tion. But  on  theory  it  may  be  conjectured  that  the 
recurrences  stand  only  in  relation  to  orbital  movements.* 
A  study  of  the  densities  of  these  satellites  affords  some 
very  suggestive  results.  The  densities  have  been  already 
included  in  a  table  of  the  satellites  on  page  435.  Taking 
the  earth's  density  as  unity,  they  range  from  one-fifth  to 
two-fifths.  The  density  of  our  moon  is  three-fifths.  Sat- 

*  Father  Secchi,  nevertheless,  states  that  he  has  observed  a  rotation  of  some 
of  Jupiter's  satellites  (Le  Soleil,  ii,  405). 


JUPITER;  441 

ellite  IV,  which  has  about  the  mass  of  the  moon,  has  less 
than  half  its  density.  Satellite  III,  with  two  and  a  quar- 
ter times  the  mass  of  the  moon,  has  little  more  than  half 
its  density.  Now,  as  these  satellites  cannot,  with  any 
probability,  be  regarded  as  enshrouded  in  warm  vapors, 
or  even  in  a  high  thermal  state,  they  are  in  a  fair  condi- 
tion to  compare  with  our  moon;  and  when  we  find  them 
possessing  a  greatly  lower  density  than  our  moon,  we  are 
constrained  to  believe  them  composed  of  lighter  materials. 

Again,  Jupiter  and  his  satellites  might  be  conceived  as 
formed  of  materials  of  nearly  the  same  density.  But  as 
Jupiter  possesses  59,250  times  the  mass  of  the  first  satel- 
lite, and  11,310  times  the  mass  of  the  largest  satellite,  the 
vast  condensation  existing  in  his  interior  should  give  him 
a  much  greater  density  than  any  of  his  satellites.  But, 
on  the  contrary,  his  density  is  only  one-fourth  that  of 
the  earth.  This  remarkable  fact  affords  further  indication 
of  Jupiter's  high  thermal  state. 

If,  as  we  argue,  the  materials  of  Jupiter's  satellites 
embrace  a  larger  proportion  than  the  earth  of  aqueous 
and  gaseous  compounds,  then  the  solid  and  cooled  body  of 
one  of  these  satellites  would  be  less  capable  of  effecting 
a  complete  absorption  of  the  fluids,  as  has  taken  place  on 
our  moon.  It  is,  indeed,  quite  supposable  that  the  fluids 
should  exist  in  sach  proportion  as  to  suffice  for  saturating 
the  pores  of  the  cooled  planet,  and  supplying  a  surplus  to 
cover  its  surface.  We  must  bear  in  mind,  then,  the 
possibility  that  these  and  other  and  remoter  satellites 
of  our  system  remain  actually  water-covered.  A  vapor- 
laden  atmosphere  might  possibly  restrain  within  it  suffi- 
cient solar  heat  to  keep  such  a  watery  film,  or  partial  film, 
in  a  state  of  liquidity;  but,  on  the  contrary,  it  is  almost 
certain  that  the  thin  atmosphere  of  these  light  bodies 
admits  of  radiation  so  free  that  any  surface  water  is  held 
permanently  in  a  solid  state.  The  possibility  of  fields  of 


442  SPECIAL  PLAKETOLOGY. 

ice  ocean-wide  renders  it  possible  that  the  sun's  light 
should  be  flashed  to  us  in  certain  situations  of  the  satel- 
lite, giving  it  a  temporary  excess  of  brilliancy.  Wide 
areas,  with  only  the  reflecting  power  of  crushed  ice  or 
Alpine  neve,  might,  by  contrast  with  the  darker  upland 
areas,  as  is  aptly  illustrated  by  the  snow-covered  polar 
regions  of  Mars,  produce  that  variation  in  reflecting 
power  which,  otherwise,  I  have  attributed  to  mere  topo- 
graphical configuration. 

§6.     THE  ULTRA-JOVIAN  PLANETS. 

Much  that  has  been  said  of  Jupiter  may  be  applied 
with  even  increased  propriety  to  all  the  planets  exterior  to 
him.  The  ringed  planet  with  a  diameter  more  than  nine- 
elevenths  the  diameter  of  Jupiter,  has  less  than  one-third 
of  his  mass,  and  possesses,  consequently,  only  half  its 
density,  or  .129  that  of  the  earth.  This  is  only  three- 
fourths  the  density  of  water;  while  Jupiter  possesses  one 
and  three-eighths  the  density  of  water.  Gravity  at 
Saturn's  surface  is,  therefore,  1.14  that  on  the  earth. 
Moreover,  the  surface  of  Saturn  is  veiled  in  clouds  like 
that  of  Jupiter,  and  analogous  belts,  though  fainter,  are 
generally  seen  drawn  across  his  disc.  His  relative  lumin- 
osity is  but  a  little  less  than  Jupiter's.  The  condition  of 
Saturn  is,  therefore,  more  extraordinary  than  that  of  Jupi- 
ter. If  we  found  reason  for  supposing  the  latter  to  sub- 
sist still  in  a  primitive  and  highly  heated  stage,  the  con- 
clusion seems,  at  first  thought,  even  better  suited  to  the 
case  of  Saturn.  It  must  be  admitted  that  in  the  case  of 
both  these  planets  thermal  intensity  would  suffice  to  pro- 
duce the  low  density  observed,  only  on  the  supposition 
that  it  approaches  somewhat  that  of  the  sun,  whose  den- 
sity is  the  same  as  Jupiter's,  and  twice  that  of  Saturn. 
But  a  heat  approaching  that  of  the  sun  is  entirely  inadmis- 


THE   ULTRA-JOVIAN   PLAKETS.  443 

sible,  since  this  would  dissipate  the  aqueous  vapors  which 
envelop  these  planets,  and  would  impart  to  their  light 
spectroscopic  properties  truly  solar.  There  is  no  probable 
way  of  accounting  for  the  low  density  of  Saturn  but  to 
admit  that  it  is  composed,  in  larger  proportion  than  the 
earth,  of  substances  possessing  a  low  specific  gravity. 
This  conviction  carries  our  thoughts  back  to  the  primitive 
nebular  condition  of  our  system,  and  recalls  a  conclusion 
of  which  we  have  heretofore  been  frequently  reminded, 
that  the  denser  matters  would  gravitate  toward  the  centre 
of  the  nebula,  leaving  the  lighter  to  enter  into  the  forma- 
tion of  the  earlier  planetary  rings.  Then  it  is  supposable, 
also,  that  Saturn  still  lingers  in  a  high  thermal  stage,  and 
that  his  cloudy  envelope,  like  that  of  Jupiter,  depends  on 
the  action  of  internal  heat,  and  argues  the  stage  of  the 
cosmic  rainstorm  on  the  planet's  surface.  All  the  evi- 
dences of  primitive  thermal  conditions  which  have  been 
pointed  out  in  Jupiter  and  his  satellites  are  repeated  in  the 
system  of  Saturn,  except  that  Saturn'1!*  double  age  intro- 
duces a  changed  relation. 

Of  the  planets  Uranus  and  Neptune,  our  information 
is  comparatively  imperfect.  They  are,  however,  well  known 
to  be  of  nearly  equal  volume  and  density,  having  diameters 
less  than  half  that  of  Saturn,  and  densities  approximating 
that  of  Jupiter.  They  are  thus  but  little  denser  than  water.* 
The  inherent  luminosity  of  Uranus  is  even  greater  than 
Jupiter's,  and  that  of  Neptune  is  equal  to  Saturn's.  It  is 
the  opinion  of  Proctor  that  the  reasons  for  assigning  a 
high  thermal  condition  to  Jupiter  constrain  us  to  reach  a 
similar  conclusion  in  reference  to  these  planets. 

This  conclusion,  however,  is  not  the  only  one  to  be  sug- 
gested. The  theory  of  partial  incandescence  in  Jupiter  is 

*The  Annualre  du  Bureau  des  Longitudes  for  1881,  however,  gives  the  den- 
sity of  Xeptune  as  .410  compared  with  the  earth,  while  that  of  Uranus  is  .234, 
and  that  of  Jupiter  .242. 


444  SPECIAL    PLANETOLOGY. 

admissible.  But  Saturn  is  both  an  older  planet  and  a 
smaller  one.  It  should  be  further  advanced  in  its  evolu- 
tion. But'  its  density  is  even  less  than  that  of  Jupiter. 
We  cannot  pursue  the  line  of  reasoning  employed  in 
Jupiter's  case,  and  infer  still  higher  incandescence  than 
we  may  admit  in  Jupiter.  The  embarrassment  is  repeated 
and  augmented  as  we  recede  from  Saturn  to  Uranus,  and 
from  Uranus  to  Neptune.  We  seem  constrained  to  seek 
some  other  explanation  more  in  harmony  with  the  doctrine 
of  successiveness  in  planetary  origins  and  the  necessity  of 
some  relation  between  age,  amount  of  internal  heat,  and 
rate  of  cooling. 

The  great  facts  in  the  case  of  the  three  outer  planets 
are  enormous  bulk,  low  density,  exceptional  brilliancy  and, 
as  is  probable,  great  relative  age.  Any  hypothesis  con- 
cerning their  physical  condition  must  harmonize  these  four 
facts.  Now,  our  theory  requires  a  gradation  in  densities 
corresponding  with  approximation  toward  the  centre  of 
the  system.  The  superior  age  of  the  remoter  planets 
requires  them  to  be  more  advanced  in  their  evolution,  and 
their  superior  mass  requires  them  to  be  less  advanced. 
Their  actual  condition  is  the  resultant  of  these  two  require- 
ments, and  it  may  not  be  possible  to  ascertain  whether  it 
is  a  stage  of  world-life  more  or  less  advanced  than  that  of 
the  earth. 

Apparently,  however,  strong  reasons  exist  for  regarding 
the  ultra-Jovian  planets  as  far  more  advanced  than  the 
earth.  An  attempt  to  calculate  the  relative  duration  of 
their  cosmic  periods  brings  out  unexpected  results.  Any 
precise  calculation  is  impossible,  in  consequence  of  their 
relatively  low  density  and  the  impossibility  of  ascertaining 
their  true  volumes,  arising  from  the  vapors  which  con- 
ceal the  true  planetary  bodies.  But,  assuming  the  dimen- 
sions of  these  planets  to  be  such  as  are  usually  given  in 
the  tables,  and  making  the  calculations  according  to  the 


THE    ULTRA-JOVIAN    PLAXETS.  445 

principles  heretofore  explained,  we  find  that  the  cosmic 
periods  of  Saturn  exceed  those  of  the  earth  by  only  one- 
seventh,  while  Uranus  and  Neptune  have  cosmic  periods 
of  only  three-quarters  the  length  of  the  terrestrial  periods. 
Those  planets  held  primitively  many  times  the  quantity  of 
heat  possessed  by  the  primitive  earth,  but  their  relative 
surfaces  gave  them  power  of  radiation  in  equal  or  greater 
ratio.  It  has  been  generally  conceived  that  cosmic  periods 
were  longer  on  all  the  remoter  planets,  but,  after  allowing 
for  all  chances  of  error  in  calculation,  it  appears  certain 
that  the  ultra-Jovian  planets  advanced  at  about  as  rapid  a 
rate  as  the  earth.  Their  vastly  superior  age  seems,  then, 
to  afford  very  strong  evidence  that  they  have  not  only 
passed  the  Jovian  stage,  but  even  the  terrestrial.  The 
vapors,  therefore,  which  envelop  them  cannot  arise  from 
any  heat  comparable  with  that  supposed  to  be  perpetuated 
in  the  planet  Jupiter. 

Now,  will  it  be  allowable  to  entertain  these  concep- 
tions of  Saturn,  Uranus  and  Neptune,  and  hold  at  the  same 
time  to  the  partial  incandescence  of  Jupiter?  Can  we 
maintain  heat  as  the  cause  of  Jupiter's  low  density,  and  a 
cooled  aqueous  condition  as  the  cause  of  the  low  density 
of  the  remoter  planets?  This,  I  admit,  is  a  question 
which  ought  to  be  considered  open.  Perhaps  Jupiter, 
also,  is  a  cooled  aqueous  globe,  instead  of  a  globe  in  its 
high  thermal  and  stormy  stage.  Assuredly,  we  must  con- 
cede to  Jupiter  a  much  larger  proportion  of  water  and 
gases  than  the  earth  possesses;  but  must  we  affiliate  the 
planet  in  constitution  and  stage  of  development  with 
Saturn  more  than  with  the  earth  and  a  certain  stage  in  its 
life  history?  In  passing  from  Jupiter  to  Saturn  the  dis- 
tance is  more  than  doubled  which  separates  Jupiter  from 
us.  If  the  interval  which  separates  Jupiter  from  us  justi- 
fies all  the  assumed  contrast  in  conditions  which  has  been 
indicated,  the  greater  distance  between  Jupiter  and  Saturn 


446  SPECIAL    PLANETOLOGY. 

justifies  an  equal  contrast,  and  all  the  more  when  we  con- 
sider that  Jupiter's  cosmic  periods  are  twice  the  length  of 
Saturn's.  But  the  comparison  is  not  alone  between  Jupi- 
ter and  Saturn,  but  between  Jupiter  and  the  group  of 
remoter  planets.  What  does  the  mean  distance  of  this 
group  from  Jupiter  suggest  and  demand  in  reference  to 
comparative  conditions'?  What  does  the  extreme  dis- 
tance demand?  Uranus  is  four  times  as  remote  from  the 
earth  as  Jupiter  is,  and  Neptune  is  more  than  seven  times 
as  remote.  There  is  space  for  enormous  contrasts  of  con- 
ditions, even  with  cosmic  periods  as  long  as  Jupiter's. 

If  Saturn  is  composed  of  materials  less  dense  than 
those  which  make  up  the  bulk  of  our  earth,  what  are 
those  materials  likely  to  be  except  water,  atmospheric  air, 
perhaps  with  the  constituents  mixed  in  different  propor- 
tions, gaseous  hydrocarbons  and  carbonic  anhydride? 
In  addition,  there  must  be  smaller  proportions  of  the 
various  solid  constituents  of  the  earth.  If  Saturn  were 
composed  wholly  of  water,  his  density  would  be  greater 
than  it  is  in  consequence  of  central  condensation.  If  he 
possessed,  in  addition,  a  superior  allotment  of  gaseous 
constituents,  they  would  clothe  the  watery  globe  with  an 
atmosphere.  In  the  centre  of  the  globe  of  water  would 
be  accumulated  all  the  solid  constituents.  Incrustation 
would  be  the  freezing  of  an  icy  film  upon  the  watery  sur- 
face; but  it  would  begin  late  and  only  at  a  much  lower 
temperature  than  rocky  incrustation.  The  prolonged 
liquidity  of  the  planet  would  prolong  the  process  of  con- 
vective  cooling,  and  thus  accelerate  planetary  refrigera- 
tion beyond  the  rate  already  indicated.  So  old  a  planet 
cooling  by  convection  should  have  passed  the  thermal 
stage.  Enormous  internal  condensation  might  deprive 
some  of  the  watery  mass  of  the  properties  of  a  liquid, 
and  thus  arrest  partially  the  convective  process,  while 
Cooling  would  proceed  by  radiation  from  the  surface. 


THE    ULTRA-JOVIAN    PLANETS.  447 

The  incidents  in  the  formation  of  an  icy  crust  would  pre- 
sent a  complete  analogy  with  the  history  of  terrestrial 
incrustation.  A  watery  planet  would  never  absorb  com- 
pletely its  atmosphere,  especially  if  we  assume  a  greater 
relative  volume  on  such  a  planet.  At  all  stages  of  cool- 
ing, therefore,  a  voluminous  atmosphere  would  be  present, 
and  at  all  temperatures  the  vapor  of  water  would  rise  and 
load  the  atmosphere  with  clouds.  The  cloudy  envelope 
would  increase  the  apparent  diameter  of  the  planet,  and 
lead  to  an  underestimate  of  its  density.  Even  with  the 
central  condensation  due  to  the  mass  of  Saturn,  the  actual 
mean  density  might  not  be  greater  than  what  we  actually 
observe.  At  the  same  time  the  reflecting  power  of  the 
cloudy  envelope  might  impart  to  the  planet  that  extra- 
ordinary degree  of  luminosity  which  Zollner  has  deter- 
mined. The  relative  brilliancy  of  Saturn  ought,  in  this 
view,  to  be  much  greater  than  that  of  the  rocky  disc  of  the 
moon.  If  these  considerations  are  applicable  to  Saturn, 
they  are  quite  as  applicable  to  Uranus  and  Neptune. 
Uranus  is  said  to  present  some  spectroscopic  indications 
of  a  peculiar  character.  In  reference  to  this,  we  can 
understand  that,  according  to  our  theory,  the  two  outer 
planets  should  contain  progressively  more  of  the  gaseous 
constituents,  but  this  is  all  which  can  at  present  be 
suggested. 

Should  the  views  here  set  forth  be  true  respecting  the 
excess  of  watery  and  aeriform  constituents  in  these  plan- 
ets, then  tidal  action  upon  their  surfaces  could  never  have 
produced,  since  their  fire-mist  stage,  the  retardative  effects 
experienced  by  planets  which  pass  long  periods  in  a  state 
of  molten  viscosity.  As  long,  also,  as  their  waters  main- 
tained an  unfrozen  state,  the  retardative  action  of  their 
tides  would  be  small  compared  with  terrestrial  oceanic 
tides,  since  no  continental  barriers  to  tidal  motion  would 
be  interposed,  and  the  only  retardation  would  arise  from 


448  SPECIAL    PLAXETOLOGY. 

the  low  viscosity  of  water.  When  incrustation  (ice  forma- 
tion) began,  even  this  action  of  watery  tides  would  be 
greatly  diminished,  and  would  finally  cease.  Much,  there- 
fore, of  the  primitive  rotational  velocity  of  such  planets 
must  be  retained  to  the  present  epoch.  This  inference 
agrees  with  our  best  observations. 

In  view  of  these  considerations,  it  does  not  seem  a 
violent  supposition  to  assume  an  aqueous  and  cold  condi- 
tion for  Neptune,  and  a  semi-aqueous  and  heated  condi- 
tion for  Jupiter.  Then,  further,  the  similarity  of  the 
indications  from  Saturn,  Uranus  and  Neptune  is  signifi- 
cant. If  they  were  still  in  planetary  progress  they  would 
not  exhibit  the  same  stage  of  evolution.  How  could 
identity  of  condition  exist  unless  that  condition  be  a 
planetary  finality?  No  planet  can  pass  a  state  of  total 
refrigeration.  Perhaps  Neptune  attained  this  and  re- 
mained changeless.  Uranus  later  attained  it  and  remained 
changeless.  Saturn,  even,  has  attained  it,  and  the  three 
oldest  planets  accordingly  have  run  their  courses  equally, 
and  have  alike  attained  the  death  which  levels  all  dis- 
tinctions. 

Under  any  theory  the  four  remoter  planets  present 
existing  conditions  widely  different  from  those  of  our 
planet.  In  the  view  here  suggested,  the  three  remoter 
planets  evince  conditions  of  constitution  so  diverse  from 
those  of  the  earth  that  the  terrestrial  state  can  never  have 
been  assumed,  though  the  terrestrial  stage  may  long  since 
have  been  passed.  These  planets  roll  on  through  the  still 
and  changeless  winter  of  their  planetary  life  —  globes  of 
crystal  wrapped  in  stagnant  fogs  which  the  sun's  feeble 
ray  is  unable  to  stir  to  the  movements  which  characterize 
a  living  world. 


THE    ULTRA-JOVIAN    PLAXETS. 


449 


jiil 


Radius,    miles, 
and  Earths  1. 


J_8_ 


Surface. 
Earth  =  1. 


Volume. 
Earth  =1. 


8  i    8 


u  i  2 


Mass.  Earth=l 


Density. 
Earth  =  1. 


»l 


ti 


III 


Solar  Intensity. 
Earth=l  at 


f*£i^ 


Cosmic  Periods. 
Earth=l 


Solar  Tidal 
Efficiency. 
Earth=l. 


Linear   fluctua- 
tion of  Solar- 
tide. 
Earths  1. 


Atmospheric 
Pressure. 
Earth=l. 


I   I 


Height   of 
Barometer. 
Earth =30. 


Water  boils. 
Earth=212° 
Fahr. 


a    Height  of 
—  5.      Homogeneous 
Atmosphere. 


450  SPECIAL   PLANETOLOGY. 

Remarks  on  the  Table  of  Planetogenic  Constants. 

1.  The  "cosmic  periods"  are  identical  with    relative 
intensities  of  gravity  on  the  surfaces  of  the  planets;  since 
g'=  g  •  ^  •  — ,  where  g' ,  m  and  r  are  gravity,  mass  and 
radius  of  the  planet,  and  g,  M  and  R  are  gravity,  mass  and 
radius  of  the  earth.     But  this  expression  is  equivalent  to 
0 "  2  *  §»  where  s  and  S  are  surfaces.      But,  making  the 
terrestrial  values  g,  M  and  S  equal  to  unity,  we  have  for 
relative  gravity,  g'  =  j,  which  is  identical  with  the  expres- 
sion for  relative  cosmical  periods. 

2.  The  "linear  tidal  fluctuations"  are  intended  to  show 
what  would  take  place  on  ocean-covered  bodies  similar  to 
the  earth,   and  not  to  imply  that  such  tides  have  ever 
actually  existed,  in  each  case,  or  ever  will   exist.     Still, 
about  this  we  can  neither  affirm  nor  deny  positively.    They 
stand,  at  least,  as  measures  of  tidal  forces  and  tidal  effects 
in  some  form. 

3.  The  values  entered  in  the  last  four  Columns  cannot 
be  very  exact.     They  rest  on  the  assumption  of  physical 
conditions  analogous  with  those  of  the  earth;  but  this  we 
know  is  not  generally  the  fact.     Besides  the  differences  in 
the  ratios,  in  different  parts  of  the  system,  between  the 
fluid  and   solid  constituents,  the  differences   in   thermal 
conditions  and  states  of    matter  vitiate  the  results   ob- 
tained, especially  in  regard  to  the  remoter  planets  and  the 
sun.     The  same  is  true  respecting  the  column  of  cosmic 
periods.    Still  all  these  results  are  suggestive  and  interest- 
ing. 


CHAPTER  IV. 

PLANETARY    DECAY, 

OR   COSMIC    CONDITIONS   MORE   ADVANCED    THAN   THE 
TERRESTRIAL    STAGE. 

Physico-mechanical  laws  are,  as  it  were,  the  telescopes  of  our  spiritual  eyes 
which  can  penetrate  into  the  deepest  night  of  time,  past  and  to  come.— HELM - 

HOLTZ. 

Everything  cosmical  must  be  gradually  decaying. — P.  G.  TAIT. 
§1.     EXTREMELY  ERODED  CONDITIONS. 

rTIHE  erosion  of  the  terrestrial  surface  has  been  in 
-L.  progress  ever  since  the  emergence  of  the  oldest  land. 
The  chief  erosive  agents  are  waters,  frosts  and  winds. 
The  action  of  these  agents  is  everywhere  facilitated  by 
changes  in  the  state  of  cohesive  and  chemical  aggregation 
of  the  parts.  The  forces  of  cohesion  and  chemism  are 
influenced  by  temperature,  and  this  sometimes  varies  with 
the  rate  of  escape  of  heat  from  the  planet's  interior.  The 
total  amount  of  erosion  which  the  earth's  surface  has 
endured  is  measured  by  the  total  amount  of  sedimentation 
which  has  taken  place  since  land  first  appeared.  The  whole 
mass  of  the  existing  sedimentary  rocks  measures  only  a 
part  of  this  denudation,  since  older  sedimentary  rocks 
have  been  repeatedly  reduced  to  sediments  and  reelevated 
in  later  ages.  Not  only  have  vast  volumes  of  earlier  sedi- 
mentary formations  been  worn  out  and  rewrought  into 
later  formations,  but  the  entire  mass  of  the  primitive  fire- 
formed  crust  has  disappeared  —  on  its  lower  surface  by 
refusion,  but  on  its  upper  surface  by  erosion  and  chemical 
dissolution. 


452  PLANETARY    DECAY. 

During  the  progress  of  these  erosions,  mountain  masses 
have  shrunken  in  dimensions,  continental  surfaces  have 
been  lowered,  and  oceanic  basins  have  been  progressively 
filled  —  more  especially  along  the  continental  borders. 
There  are  good  geological  grounds  for  believing  that  ex- 
tensive land  areas  have  disappeared  * —  partly  by  erosion, 
but  sometimes  by  subsidence  —  while  the  progressive 
emergence  of  the  principal  continental  masses  has  been 
going  forward.  All  geological  evidence,  however,  points 
toward  the  conclusion  that  no  general  interchange  of 
oceanic  and  continental  regions  has  ever  taken  place. 

The  first  effects  of  terrestrial  erosions  lie  exposed  to 
our  observation  on  a  vast  scale.  Some  of  these  are  results 
whose  earlier  history  reaches  back  into  the  middle  or  begin- 
ning of  Mesozoic  Time.  The  old  Niagara  gorge  began, 
probably  as  soon  as  the  drainage  course  was  established 
from  the  Superior  Sea  to  the  Gulf  of  St.  Lawrence.  This 
could  have  been  even  in  Palaeozoic  Time.  The  Ohio, 
Upper  Mississippi,  Hudson,  Connecticut  and  many  other 
river  valleys  began  to  be  excavated  at  epochs  equallv 
remote.  The  work  in  all  such  cases  has  been  in  progress 
to  the  present  time,  except  so  far  as  interrupted  by  the 
conditions  of  the  Glacial  Period.  In  our  trans-Mississippi 
states  and  territories  are  records  of  erosion  equally 
ancient.  But  the  most  conspicuous  cases  probably  date 
from  the  Mesozoic  or  Csenozoic  Time.  The  stupendous 
canons  of  the  Colorado,  Green,  Columbia  and  other  west- 
ern rivers  are  features  Mesozoic  or  Crenozoic  in  their  ori- 
gin, but  progressively  worked  out  by  agencies  which,  to 
our  day,  have  never  ceased  their  activity,  however  their 
forces  are  diminished;  as  the  monuments  of  the  genius  and 
power  of  classic  Greece  connect  themselves  by  historic 
continuity  with  the  feebler  activities  of  modern  Greeks 
exerted  under  the  observation  of  the  world.  The  broad, 

*  Sec  the  author's  Sparks  from  a  Geologist's  Hammer,  122-51. 


EXTREMELY  ERODED  CONDITIONS.        453 

scarred  and  desolated  plateaus  of  the  West  testify  to  the 
removal  of  thousands  of  cubic  miles  of  the  ancient  sur- 
face. Some  of  the  greatest  of  these  denudations  have 
taken  place  in  later  Tertiary  time.  The  records  of  erosions 
begun  in  a  later  geological  period  are  universally  exposed 
to  view.  All  except  the  fundamental  features  of  our 
topography  have  been  carved  out  by  erosive  agencies  in 
post-glacial  times. 

The  mode  of  action  of  these  agents  is  matter  of  daily 
observation.  Every  turbid  summer  torrent  reveals  the 
transportation  of  portions  of  the  disintegrated  surface  of 
the  earth  from  higher  to  lower  levels.  Some  of  these 
sediments  find  their  way  into  the  bottoms  of  lakelets  and 
build  up  the  foundations  of  marshes  and  alluvial  lands. 
Some  are  borne  to  the  larger  streams  to  be  deposited  on 
their  flooded  flats,  or  carried  to  the  Missouri,  the  Ohio  and 
the  Mississippi.  The  Mississippi,  like  the  Amazons,  the 
Ganges  and  the  Nile,  contributes  its  annual  layer  to  a 
thickening  delta,  and  bears  the  remainder  of  its  sediment- 
ary burden  to  the  sea.  In  the  Gulf  of  Mexico  it  builds  a 
bar  by  the  annual  accumulation  of  sediment,  which  in  "its 
growth  has  encroached  sea-ward  338  feet  a  year.  It  has 
already  grown  far  from  the  ancient  Gulfshore,  and  carried 
its  foundations  into  the  deep  waters  of  the  Gulf.  Dr.  J. 
E.  Hilgard  has  shown  that  the  deep  basin  of  the  Gulf 
approaches  very  near  to  the  present  bar  and  present  ter- 
mination of  the  jetties  of  Eads.* 

By  such  erosions  and  transportations  the  continents  are 
continually  lowered  and  the  sea  basins  are  repleted  with 
materials  taken  from  the  land.  If  elevatory  forces  were 
as  efficient  as  formerly,  the  relative  levels  of  the  land  and 

*J.  E.  Hilgard:  The  Basin  of  the  Gulf  of  Mexico,  "Science"  ii,  138-40, 
March  36, 1881,  with  a  chart.  The  depth  of  the  water  into  which  the  bar  has 
reached  will  cause  hereafter  a  slower  development  than  in  earlier  times.  The 
efficiency  of  the  jetties  will  therefore  remain  without  serious  diminution,  for  a 
period  comparatively  prolonged. 


454  PLANETAKY    DECAY. 

sea  bottom  might  be  retained;  and  the  relative  altitude  of 
the  land  might  be  increased.  But  the  elevatory  forces 
must  undergo  diminution,  and  the  continents  must  conse- 
quently be  slowly  transferred  to  the  ocean  basins.  If  the 
amount  of  surface  water  remains  undiminished,  the  sea 
level  must  slowly  rise,  and  the  time  must  come  when  the 
fuller  ocean  will  overflow  the  shrunken  dimensions  of  the 
land.  When  the  work  of  erosive  agencies  is  accomplished, 
the  sea  will  be  universal,  as  it  was  before  the  nuclear 
wrinkles  of  the  continents  first  emerged.  The  earlier  and 
the  later  conditions  of  our  planet,  therefore,  present  it 
wrapped  in  a  sheet  of  water.  The  continental  lifetime  is 
only  a  temporary  emergence  of  sea  bottom  accompanying 
slight  movements  occasioned  by  stresses  of  the  earth's 
interior.  Organization  seizes  the  opportunity  to  rest  its 
foot  on  the  unsteady  land;  it  plays  its  evanescent  role, 
and  the  continental  swell  settles  back  into  the  ancient  bed 
from  which  it  lifted  its  head  only  for  a  temporary  relief. 
The  ancient  ocean  still  lives;  the  tidal  wave  still  rolls;  the 
sun  rises  and  sets  as  before;  the  moon  waxes  and  wanes: 
the  storms  in  the  atmosphere  have  died;  the  sounds  of 
animated  nature  have  perished;  life  conceals  its  perpetu- 
ated activites  in  the  voiceless  depths  of  the  all-subduing  sea. 
In  the  annexed  diagram  A  B  represents  the  mean  level 
of  the  land,  E  F,  the  present  sea  level  and  CD,  the  sea 
bottom.  When  the  continents  have  been  levelled  to  the 
present  water's  surface  E  P,  the  ocean  will  stand  at  I  K, 
282  feet  deep  over  all  the  land.  The  land  above  the  pres- 
ent ocean  level,  if  thrown  into  the  sea,  would  raise  its  bot- 
tom to  G  H,  384  feet,  These  results  rest  on  Keith  Johnson's 
estimate  of  about  one-fifth  of  a  mile  for  the  mean  height 
of  the  land.  If  we  take  Krlimmel's  more  recent  esti- 
mates,* we  shall  have  the  mean  elevation  of  Europe  300 

*Krflmmel,  Gdttinger  Acad. ;  O.  Leipoldt,  Petermann's  Mittheilungen, 
Apr.,  1875,  Nature,  15  Apr.,  1875,  and  3  Feb.,  1879,  348-9:  Amer.  Jour.  Sci.,  III. 
lx.482. 


EXTREMELY    ERODED    CONDITIONS. 


455 


m.,  Asia  and  Africa,  500m.,  America,  330m.,  Australia 
250m.,  giving  a  mean  of  426m.,  or  .2646  mile.  This 
would  cause  the  ocean  to  stand  at  IK  373  feet  above  its 


& 

373  

JK 

1  1 



i  i 

0 
L  

—  -p 

1 
M 

3 

< 

F 

[ 

1M 

C  D 

FIG.  59.  THE  DISAPPEARANCE  OP  THE  LAND. 

present  level,  if  all  the  land  were  thrown  into  the  sea,  and 
the  sea  bottom  would  be  raised  to  G  H,  509  feet. 

The  plane  M  N  which  has  an  amount  of  land  above  it 
equal  to  the  capacity  of  the  ocean's  basin  below  it  —  that 
is,  the  plane  which  would  represent  the  surface  of  the 
land  if  it  were  completely  levelled  down,  passes,  if  we  take 
Keith  Johnson's  estimate  of  the  mean  altitude  of  the  land, 
1.42  miles  —  the  distance  P  M'  —  below  the  present  level 
of  the  sea;  or  if  we  take  Krilmmel's  estimate,  1.41  miles. 
Hence  a  complete  levelling  of  the  land  surface  would  cause 
the  sea  to  stand  9541  feet  above  the  land,  according  to 
Keith  Johnson's  data,  or  9450  feet,  according  to  Krilm- 
mel's estimate  of  the  present  mean  height  of  the  land. 
The  deposit  of  this  amount  of  land  on  the  ocean's  bottom 
would  raise  it  to  M  N,  3860  feet,  or  3950  feet,  according 
to  the  data  used.* 


Let  /  =  relative  surface  of  land  =  .167, 
w  =  relative  surface  of  water  =  .733, 

h  =  mean  heightof  land  =  E  A  = 


456  PLANETARY    DECAY. 

Such  are  the  tendencies  of  erosive  agencies  on  the  ter- 
restrial surface,  and  such  tendencies  must  exist  wherever 

d  =  mean  depth  of  ocean  =  P  C  =  2.538  miles, 
z  =  depth  of  uniform  land  surface  below  present  sea  level  =  E  M, 
y  =  depth  of  sea  over  uniform  land  surface  —  M  I,  as  appears, 
c  —  C  G  —  depth  of  covering  on  sea  bottom  when  land  is  lowered  to  E  P, 
c'  =  M'C  =  depth  of  covering  on  sea  bottom  when  land  is  lowered  to  M  N, 
x  =  E  I  =  rise  of  sea  level  when  land  is  lowered  to  E  P, 
x'  =  rise  of  sea  level  when  land  is  lowered  to  meet  sea  level. 
I.  Suppose  land  levelled  to  E  P,  the  present  sea  level. 
Then  x  (w  +  1)  =  Ih,  or,  since  ID  +  I  =  1, 

*  =  I  A  =  .267  X  -[  i,,,  f  =  -!  ;gg*  SS  H  B  feet  f  ab°Ve  »M  8Ca  lOTe1' 


of  deposit  on  ocean's  floor. 

II.  Suppose  land  levelled  to  meet  rising  sea  level. 

Then  I  (h  —  a?)  =  wx',  whence  of  =  —  —7  =  I  h  -  a;  as  above. 

III.  Suppose  the  land  levelled  to  uniform  land  surface  M  X. 

Now,  the  land  surface  will  be  even  all  over  the  globe  ;  the  present  volume 
of  the  ocean  will  be  of  uniform  depth,  and  we  shall  have 

y  (w  -f-  1)  —  wd,  or,  since  w  -\-  I  =  1, 

y  =  wd  =  .733  X  2.538  miles  =  1.8604  mile  =  depth  of  sea  all  over  the  earth. 
Also  to  find  E  M,  depth  of  uniform  land  surface  below  the  present  sea  level, 
I  (h  -f  z)  =  w  (d  —  z)  and  Iz  —  wz-wd  —  lh. 

•••  '  =  J7Ti£=  *«-»-«••*  ^8  -  .*"  X  {  ^  =  {  {;«J™  f     mile 
=  depth  below  present  sea  level  of  uniform  land  surface, 

sulting     sea    level    above 


present  sea  level  =  x  =  x'. 

That  is,  the  depth  of  the  overflow  is  the  same  as  when  the  land  is  levelled 
only  to  the  present  sea  level.  This  must  obviously  be  so,  since  after  the  level- 
ling of  the  land  meets  the  rising  sea  level,  all  further  lowering  of  the  land  is 
simply  a  change  of  place  of  matter  within  the  mass  of  ocean  waters.  Hence  the 
line  of  meeting  of  the  lowering  land  surface  and  the  rising  sea  level  ought  to 
be  as  shown  above,  -j  JSZ  r  feet  above  present  sea  level.  This  is  the  highest 
which  the  sea  level  can  be  made  to  attain. 

Also,  to  find  M'C,  the  depth  of  the  deposit  over  the  ocean's  floor, 


J6?  ''   """T  *•"*».    =  )  .7311  mue  |.  =  j  *»u  reei  ^  depth  over  ocean-g  floor  = 

.7-M 

M'C. 

But  this  is  also  given  directly,  since  M'C  =  PC  -  PM'  =  2.538  --J  }; 


EXTREMELY    ERODED    CONDITION'S.  457 

ocean  waters  are  accumulated.  On  Mercury,  and  perhaps 
also  on  Venus,  the  intensity  of  the  solar  rays  may  prevent 
water  from  existing  except  in  the  form  of  clouds.  Denu- 
dation, therefore,  could  not  have  fregun.  It  is  still  quite 
conceivable,  however,  as  before  stated,  that  the  freedom 
of  radiation  in  the  upper  atmospheres  of  both  these  plan- 
ets, and  especially  of  Venus,  may  be  such  as  to  condense 
permanent  envelopes  of  aqueous  vapor  and  thus  screen 
the  surfaces  of  the  planets  from  the  severest  intensity  of 
solar  radiation.  In  such  case,  there  must  be  also  some 
amount  of  precipitation  and  a  corresponding  amount  of 
erosion. 

Some  reasoning  as  to  the  conditions  which  may  have 
affected  precipitation  on  the  moon  have  been  presented  in 
the  section  devoted  to  the  geology  of  the  moon.  It  seems 
supposable  that  during  a  portion  of  the  moon's  non- 
synchronistic  period  vapors  condensed,  rains  fell  and  seas 
of  some  extent  existed.  The  great  tidal  influence  expe- 
rienced by  that  body,  however,  rendered  it  impossible  that 
land  masses  should  not  be  raised  to  great  altitudes  above 
the  sea  level.  The  enormous  height  of  the  tides  in  any 
extensive  ocean  must,  therefore,  have  eroded  the  shores 
and  the  bottoms  of  shallows  with  intense  energy.  If  the 
earth  was  still  a  sun  to  the  moon,  its  heat  must  have 
caused  an  extraordinary  amount  of  evaporation  and  con- 
sequent precipitation,  and  the  agency  would  have  eroded 
the  uplands  to  a  corresponding  extent.  Or,  if  water 
remained  on  the  moon  after  the  synchronistic  period  had 
been  reached, —  something  which  I  have  not  assumed, —  it 
fled  to  the  farther  side,  but  underwent  most  copious 
evaporation  through  solar  influence  during  each  alternate 
fortnight.  Great  evaporation  implies  great  precipation; 
and  it  is  hardly  supposable  that  some  of  these  rains  did 
not  fall  on  the  land  side,  and  thus  serve  as  an  efficient 
agent  of  erosion.  But  there  is  reason  to  doubt  whether 


458  PLANETARY    DECAY. 

the  moon's  surface  in  non-synchronistic  times  ever  expe 
rienced  sufficient  composure  to  allow  a  proper  ocean  to 
rest  upon  it.  Not  improbably,  the  water,  through  the 
constant  ruptures  of  the  crust,  and  outbursts  of  molten 
matter,  was  kept  in  a  constant  process  of  evaporation  and 
condensation,  until  the  solidified  portions  became  suffi- 
ciently voluminous  to  receive  the  water  into  their  pores. 
In  this  case,  the  records  of  all  aqueous  erosions  which 
ever  took  place  on  the  moon  have  become  obliterated  or 
disguised  by  the  violence  and  duration  of  eruptive  action. 
Mars  is  the  only  one  of  the  planets  besides  the  earth 
on  whose  surface  aqueous  erosions  are  somewhat  certain 
to  have  taken  place.  The  largest  of  the  satellites  of 
Jupiter,  with  a  diameter  of  about  3700  miles,  and  the  sixth 
of  Saturn,  with  a  diameter  of  3300  miles,  are  both  con- 
siderably larger  than  Mercury,  and  may  easily  be  conceived 
to  have  passed  a  thermal  condition  suited  to  aqueous  pre- 
cipitation and  erosion.  But  the  enormous  tidal  power 
exerted  on  these  sa-tellites  by  their  primaries  renders  still 
more  probable  than  in  the  case  of  our  moon,  the  hypothe- 
sis of  incessant  physical  violence  during  their  non-synchro- 
nistic period,  and  the  absence  of  all  proper  aqueous  ero- 
sion. But  the  improbability  of  erosion  on  these  satellites 
appears  still  stronger  when  we  perceive  the  probability 
that  they  are  mere  watery  globes,  or  at  least  completely 
covered  by  icy  crusts.  On  such  globes,  though  precipita- 
tions of  inconceivable  copiousness  must  have  taken  place, 
they  occurred  in  an  epoch  before  the  formation  of  the  icy 
crust.  After  its  formation  there  would  be  no  longer  any 
rainy  precipitation  or  erosive  movements  of  waters. 

§  2.   PROGRESSIVE  SUBSIDENCE  OF  TEMPERATURE. 

The  nebular  theory  implies  that  all  cosmical  spheres 
after  having  attained  the  temperature  due  to  condensation, 
begin  a  process  of  refrigeration  due  to  excess  of  radiation 


PROGRESSIVE   SUBSIDENCE   OF   TEMPERATURE.        459 

over  amount  of  heat  resulting  from  continued  transforma- 
tion of  mechanical  energy.  The  consequences  accom- 
panying the  process  of  cooling  have  been  traced  from  the 
nebular  to  the  habitable  stage;  and  incidental  references 
have  been  made  to  more  advanced  stages.  Let  us  con- 
template in  a  more  orderly  manner,  some  of  the  later  inci- 
dents of  cooling.  So  far  as  I  have  discovered,  they  reduce 
themselves  to  two  categories. 

1.  Shrinkage  and  Acceleration  of  Axial  Motion. — The 
earlier  relations  of  shinkage  to  rotary  acceleration  have 
heretofore  come  under  consideration.  But  after  a  planet 
begins  to  be  encrusted  the  method  and  the  rate  of  refrige- 
ration are  materially  changed.  In  the  fluid  state,  circu- 
latory convection  brings  the  hottest  portions  continually 
to  the  surface,  and  the  escape  of  heat  by  radiation  is 
rapid.  After  a  crust  exists,  the  fluid  within  is  protected 
from  direct  radiation.  Its  heat  imparted  to  the  crust  must 
be  conducted  through  to  the  exposed  surface  before  it  can 
be  lost  to  the  planet.  As  the  crust  thickens,  the  difficulty 
of  conduction  increases,  and  hence  the  rate  of  planetary 
cooling  diminishes.  At  a  certain  time  the  temperature  of 
the  exterior  ceases  to  be  elevated  by  the  heat  reaching  it 
from  within,  since  the  radiation  quite  equals  the  amount 
of  heat  conducted  to  the  surface.  With  the  progress  of 
time,  the  superficial  zone  of  fixed  temperature,  save  from 
climatic  influences,  deepens.  This  zone  experiences  no 
contraction  from  its  own  cooling,  but  receives  a  lateral 
pressure  arising  from  the  general  cooling  and  shrinkage  of 
the  planet.  The  consequences  of  this  are  thought  by 
some  to  be  manifest  in  plications,  crushing,  folds  and 
mountain  saliences.  A  convective  movement  of  the  inter- 
nal fluid,  if  any  exists,  may  still  be  maintained,  but  it  be- 
comes more  and  more  sluggish  as  the  crust  thickens. 
With  a  planet  as  thickly  encrusted  as  the  earth,  the  escape 
of  heat  is  extremely  slow,  and  hence  contraction  and  axial 


460  PLANETARY    DECAY. 

acceleration  are  slow.  Calculations  based  on  the  recorded 
dates  of  ancient  eclipses  indicate,  as  Laplace  thought,  that 
the  terrestrial  day  has  not  been  shortened  within  2000 
years  by  more  than  a  small  fraction  of  a  second.  This, 
however,  if  true,  is  no  disproof  of  the  existence  of  a  shrink- 
age process.  The  proper  acceleration  may  have  been  com- 
pensated by  one  or  both  of  two  causes.  First,  the  equa- 
torial protuberance  may  have  been  prevented  by  the  earth's 
rigidity  from  subsiding  at  such  rate  as  to  respond  to  the 
total  shrinkage.  The  preservation  of  the  equatorial  diam- 
eter would  largely  conserve  the  rate  of  rotation.  If  the 
subsidence  of  the  equatorial  protuberance  should  proceed 
spasmodically,  the  irregularly  varying  oblateness  of  the 
earth  might  make  itself  felt  in  irregularities  of  the  lunar 
motions  and  in  the  precession  and  other  movements  con- 
nected with  terrestrial  oblateness.  The  second  cause  com- 
pensating the  effect  of  contraction  is  the  influence  of  the 
tides,  to  which  reference  will  shortly  be  made. 

If  we  had  information  concerning  the  actual  tempera- 
ture of  the  earth's  interior,  it  would  be  possible  to  calcu- 
late, under  certain  assumptions,  the  total  amout  of  shrink- 
age which  might  result  from  any  future  refrigeration. 

2.  Absorption  of  Water  and  Atmosphere. —  I  have 
already  referred  to  the  probably  absorbed  condition  of  the 
lunar  ocean  and  atmosphere,  and  appended  in  a  note  the 
requisite  formulae  for  ascertaining  the  depth  of  crust  de- 
manded for  such  absorption  on  any  planet  constituted 
with  solids  and  fluids  in  the  same  proportion  as  the  earth, 
when  the  value  of  certain  constants  has  been  ascertained 
by  observation.  The  earth  is  the  only  planet  on  which 
observation  enables  us  to  ascertain  directly  the  values  of 
all  the  constants.  Those  accessible  only  to  direct  obser- 
vation are  the  following: 

(1.)  The  index  of  rock  absorption  by  volume.  By  this 
is  meant  the  volume  of  water  absorbable  by  one  volume  of 


PROGEESSIVE    SUBSIDENCE    OF   TEMPERATURE.       461 

the  rocky  crust  of  the  earth.  This  can  only  be  deter- 
mined by  experiments  on  rock  substances  occurring  near 
the  earth's  surface.  Such  experiments  have  been  made 
by  Durocher,*  Hunt  and  others.f  Two  methods  have 
been  employed,  one  direct,  the  other  indirect,  or  by  infer- 
ence from  the  amount  of  condensation  experienced  in 
solidification  or  through  hammering-.  Durocher  experi- 
mented on  those  minerals  which  enter  most  commonly  into 
the  constitution  of  rocks,  such  as  feldspars,  micas,  horn- 
blende and  pyroxene.  The  minerals  were  reduced  to 
coarse  powder  and  exposed  to  moist  air.  The  amount  of 
water  absorbed  was  found  by  weighings,  and  the  results 
were  as  follows:  The  orthoclase  of  Utoe  absorbed  .0041 
parts  by  weight;  seven  other  varieties  of  orthoclase  ab- 
sorbed .0128  parts;  thirty  specimens  of  various  minerals 
absorbed,  on  the  average,  .0127  parts.  A  large  number 
of  determinations  of  the  absorptive  properties  of  building 
stones  was  made  by  a  committee  of  the  British  House  of 
Commons  and  reported  in  1839.  This  committee,  of 
which  the  celebrated  geologist  Henry  de  la  Beche  was  a 
member,  employed  blocks  of  an  inch  cube,  which  were 
thoroughly  soaked  in  water  under  the  receiver  of  an  air 
pump,  and  subjected  to  the  requisite  weighings.  The  fol- 
lowing are  some  of  the  results  reduced  to  absorption  by 
volume: 

3  Silicious  Limestones,  .053,  .085,  .109. 

4  Nearly  pure  Limestones,  .180,  .206,  .244,  .310. 
4  Magnesian  Limestones,  .182,  .239,  .249,  .267. 
6  Sandstones,  .107,  .112,  .143,  .156,  .174,  .221. 
Similar  experiments  were  made  by  Professor  T.  Sterry 

Hunt  on  Canadian  rocks,  in  1864.  J     Dr.  Hunt  took  small 

*  Durocher,  Bull.  Soc.  gtol  de  France,  II,  x,  131. 

tSee  a  report  on  Building  Stones  made  to  the  British  House  of  Commons 
in  1839,  by  Barry,  de  la  Beche  and  Smith. 

JT.  S.  Hunt,  Amer.  Jour.  Sci.,  II,  xxxix,  1&3,  March,  1865;  Geology  of 
Canada.  1865,  281-4;  Canadian  Naturalist,  February,  1865,  10;  Chemical  and 
Geological  Essays,  164. 


462  PLANETARY    DECAY. 

broken  fragments  of  the  rocks  —  generally  from  300  to 
600  grains  in  weight  —  carefully  freed  from  adhering 
loose  particles,  dried  them  at  200°  Fahr.  until  they  ceased 
to  lose  weight;  noted  their  dry  weight,  left  them  in  con- 
tact with  water  for  some  hours,  and  then  kept  them  im- 
mersed in  water  under  the  exhausted  receiver  of  an  air 
pump  until  all  bubbles  disappeared;  removed  them  and 
wiped  off  superfluous  water  with  blotting  paper,  and  finally 
weighed  them,  first  in  air  and  then  in  water.  These  weigh- 
ings furnished  the  data  for  calculating,  among  other 
results,  the  index  of  absorption  by  volume.  The  results 
of  these  experiments  on  39  varieties,  mostly  of  stratified 
palaeozoic  rocks,  are  published.  A  general  view  is  given 
below: 

4  Potsdam  Sandstones,  hard  and  white,  .0139  to  .0272. 

2  Medina  Sandstones,  .0837  to  .1006. 

3  Devonian  Sandstones,  .2024  to  .2127. 

5  Shales,  .0075  to  .0794. 

6  Limestones,  .0030  to  .0527. 
11  Dolomites,  .0215  to  .1355. 

3  Tertiary  Limestones,  .2693  to  .2954. 

Nearly  all  these  experiments  relate  to  the  absorbent 
properties  of  stratified  rocks,  and  the  results  cannot  be 
taken  as  expressing  the  absorbent  power  of  the  cooled 
crystalline  crust  of  the  earth.  Some  extended  experiments 
published  by  Dr.  Hiram  A.  Cutting,*  State  Geologist  of 
Vermont,  include,  among  other  rocks,  22  varieties  of 
granite.  His  method  of  procedure  was  similar  to  that  of 
Dr.  Hunt.  He  used  samples  about  three  by  four  inches, 
and  two  inches  thick.  His  specific  gravities  are  those  of 

*  H.  A.  Cutting :  Weight,  Specific  Gravity,  Kates  of  Absorption  and  Capa- 
bilities of  Standing  Heat  of  Various  Building  Stones,  Science,  i,  254-6,  Novem- 
ber 20,  1880.  Dr.  Cutting's  results  on  the  effects  of  heat  possess  great  practi- 
cal interest.  In  this  connection,  consult  also  Gen.  Q.  A.  Gilmore's  Report,  of 
the  Compressive  Strength,  Specific  Gravity  and  Ratio  of  Absorption  of  the  Build- 
ing Stones  of  the  United  States,  8vo,  57  pp.,  1876. 


PROGRESSIVE   SUBSIDENCE   OF  TEMPERATURE.       463 

the  particles  of  the  rock  or  true  specific  gravity,  and  not 
of  the  gross  bulk  of  the  samples.  The  true  specific  gravi- 
ties of  his  samples  range  from  2.526  in  a  light-colored 
granite  from  Oak  Hill,  Maine,  to  2.833  in  a  light-colored 
granite  from  Stanstead,  Canada.  The  general  mean  is 
2.625.  The  absorption  of  one  part,  by  weight,  of  water, 
required  weights  of  granite  ranging  from  280  in  a  light- 
colored  granite  from  St.  Cloud,  Minnesota,  to  818  in  a 
gray  granite  from  Croton,  Connecticut.*  The  mean  ab- 
sorption was  one  part  of  water  for  610  parts  of  rock  by 
weight.  The  celebrated  Quincy  granite  (syenite)  stands 
near  these  means,  having  a  specific  gravity  of  2.660  and 
an  absorbent  power  expressed  by  650.  From  these  obser- 
vations it  appears  that  the  mean  index  of  absorption  by 
volume  is  .O04303.f 

*Thus  the  most  absorbent  granite  was  not  the  one  with  lowest  specific 
gravity;  nor  the  least  absorbent,  the  one  with  highest  specific  gravity.  This 
would  result  from  the  different  proportions  of  the  lighter  and  heavier  mineral 
constituents  in  the  different  granites. 

t  As  the  mean  amount  of  water  absorbed  by  one  part  of  granite  is  Vi^  by 
weight,  and  the  mean  specific  gravity  of  the  granite  is  2.625,  the  mean  volume 
of  water  absorbed  by  one  volume  of  granite  is  ^A^  X  2.625  =  .004303  =  i. 

We  may  readily  deduce  general  formulae  for  the  various  results  determina- 
ble  from  the  weighings  before  mentioned. 
Let  a  -  weight  of  dried  rock. 

6  =  difference  of  weights  of  dried  and  saturated  rock  =  weight  of  water 
which  the  rock  is  capable  of  absorbing.  Represents  the  porosity  of 
the  rock. 

c  =  loss  of  weight  in  water,  of  saturated  rock  =  weight  of  volume  of  water 
the  same  as  the  gross  volume  of  the  rock.  Represents  the  gross  vol- 
ume of  the  rock. 

Also  c  —  b  -  weight  of  water  displaced  by  net  substance  of  the  rock. 
Then  —  =  specific  gravity  of  the  gross  rock, 

— ^-r=  specific  gravity  of  the  net  rock, 


Also,  since  volumes  are  directly  as  weights  and  inversely  as  specific  gravities, 

^  _  volume  of  water  absorbed  _  weight  of  water  absorbed  X  sp.  gr.  of  rock 

gross  volume  of  rock.     ~  weight  of  rock  x  spec.  gr.  of  water. 

=  —  =  -  =  index  of  absorption  by  volume. 


464  PLANETARY    DECAY. 

Attempts  have  been  made  by  Bischof  and  MM.  Charles 
Ste.  Claire  Deville  *  and  Delesse  f  to  obtain  the  difference 
of  porosity  of  the  same  substances  in  the  liquid  and  crys- 
talline states  and  thence  to  infer  the  absorbent  properties. 
MM.  Deville  and  Delesse  showed  that  granite  on  fusion 
yields  a  glass  having  a  density  from  .09  to  .11  less  than 
that  of  the  granite.  This  means,  supposing  the  gross 
volume  to  remain  the  same,  that  a  granitic  glass  when 
crystallized  increases  the  net  specific  gravity  of  its  sub- 
stance, and  must  inclose  pores  in  its  structure  to  a  corre- 
sponding extent;  that  is,  to  about  one-tenth  of  its  gross 
volume.  Taking  the  mean  density  of  granite  at  2.625,  it 
would,  with  such  porosity,  imbibe  .03809  parts  by  weight 
for  each  part  of  granite.  J  On  similar  principles,  Dr. 

The  following  forms  are  sometimes  more  convenient : 
Let  s  =  weight  of  saturated  rock, 

s'  —  weight  of  saturated  rock  in  water. 
Then  b  =  c  —  a ;  c  =  s  —  s'  and  c  —  b  =  a  —  *'. 

—  specific  gravity  of  gross  rock, 

— — ;  =  specific  gravity  of  net  rock, 
—  8 

— —  =  index  of  absorption  by  weight, 


*  Deville,  Compt.es  Rendus,  1845. 

t  Delesse,  Bulletin  Soc.  geol.  de  France,  1847,  II,  six,  64. 
J  Some  general  expressions  for  converting  such  relations  will  often  be  found 
convenient. 
Let        g  =  specific  gravity  of  a  rock,  water  being  1, 

m  =  weight  of  water  absorbed  by  unit  weight  of  rock. 
n  —  volume  of  water  absorbed  by  unit  volume  of  rock. 
Then  mg  =  volume  of  water  absorbed  by  unit  weight  of  rock. 
Assuming  unit  weight  of  rock  as  unit  volume  of  rock, 


Hence,  further,  by  WeigM, 

If  rock  is  1,  water  absorbed  is  m. 

If  water  is  1.  rock  absorbing  it  is  —  =  -• 
m      n 

And,  by  Volume, 

If  rock  is  1,  water  absorbed  is  ». 


PROGRESSIVE   SUBSIDENCE    OF    TEMPERATURE.        465 

Frankland  has  calculated  that  the  moon  in  cooling1  through 
180°  would  create  cellular  space  equal  to  14,500,000  cubic 
miles.*  In  cooling  throughout  from  a  liquid  to  a  solid 
state,  supposing  the  liquid  to  be  represented  in  density 
by  the  solid  glass,  the  moon  would  acquire,  according  to 
the  ratio  of  porosity  found  by  Deville  and  Delesse,  528,- 
000,000  cubic  miles  of  porous  space,  f 

Saemann  has  pursued  another  indirect  method  for  ob- 
taining the  amount  of  porosity  acquired  in  passing  from 
the  liquid  to  the  solid  state.  He  assumes  that  the  poros- 
ity of  the  metals  is  due  to  molecular  shrinkage  experi- 
enced in  cooling,  and  that  the  condensation  produced  by 
hammering  is  the  measure  of  such  shrinkage.  Calculating 
from  the  increased  density  of  various  metals  produced  by 
hammering,  he  finds  that  the  porosity  of  cast  iron  is  .075; 
nickel,  .045;  aluminium,  .041;  copper,  .011;  gold,  .005. 
These  results  accord  sufficiently  well  with  those  obtained 
by  Deville  and  Delesse. 

It  is  doubtful  whether  these  methods  are  suited  for 
obtaining  the  absorbent  properties  of  rocks.  It  is  even 
highly  probable  that  all  liquefied  substances  diminish  in 
specific  gravity  in  the  act  of  solidifying;  though,  as  before 
stated,  they  may  acquire,  on  further  cooling,  a  density 
greater  than  that  of  the  liquid  magma.  The  assumed 
shrinkage  which  is  supposed  to  create  porosity  is  probably 
the  normal  shrinkage  due  to  reduction  of  temperature  con- 
siderably below  the  point  of  solidification.  The  porosity 
inferred  is  ten  times  as  great  as  that  indicated  by  direct 
experiments  on  absorption.  M.  Sremann's  assumption  also 
is  quite  gratuitous.  At  least,  it  affords  no  criterion  of  the 

If  water  is  1,  rock  absorbing  it  is  -  =  — . 

If   n  =  .1,  m  =  -  =  —. •.  =  .0:3809. 
g       g.365 

*  Frankland,  Proc.  Roy.  Inst.,  iv,  175. 
t  ±  w  x  (1080)2  x  .1  =  527,870,000  cubic  miles. 
30 


466  PLANETAKY    DECAY. 

absorbent  properties  of  the  metals.  This  is  shown  not 
only  by  the  want  of  any  cited  justification  of  the  assump- 
tion, but  by  the  fact  that  the  result  is  ten  times  as  great 
as  direct  experiment  produces. 

It  is  safest,  then  to  resort  to  direct  experiment,  and  the 
index  of  absorption  calculated  from  Dr.  Cutting's  weigh- 
ings must  be  regarded  as  the  best  present  approximation 
to  the  absorbent  power  of  the  terrestrial  crust.  This  is, 
i  =  n  =  .004303. 

(2.)  The  volume  of  the  ocean.  This  depends  on  the 
superficial  extent  and  the  mean  depth.  The  ratio  of  the 
total  land  surface  of  the  earth  to  the  total  ocean  surface 
is  generally  stated  as  1  :  2.75.  In  other  words,  the  land 
surface  is  represented  by  .267  and  the  ocean  surface  by 
.733.  This  is  the  ratio  given  in  the  Annuaire  for  1881, 
and  the  ratio  here  adopted.  Herschel  puts  the  ratio  at 
1  :  2.86,  since  the  total  water  surface  is  estimated  at  146,- 
000,000  miles  and  the  land  surface  at  51,000,000.*  Profes- 
sor Haughton  puts  the  area  of  the  sea  at  145,000,000  square 
miles,  and  the  land  at  52,000,000,  which  gives  a  ratio  of 
1  :  2.79.f  Dr.  Carpenter  adopts  the  ratio  of  1  :  2.78.J 

The  mean  depth  of  the  ocean  can  only  be  approximated. 
M.  Sagmann,  in  his  paper  already  quoted,  assumes  it  as 
600  metres,  or  1,968  feet,  which  is  a  manifest  underesti- 
mate. The  results  of  the  Challenger  and  earlier  soundings 
combined  together,  give  for  the  mean  depth  of  the  North 
Atlantic,  about  2,600  fathoms;  for  the  South  Atlantic, 
about  1,900  fathoms;  for  the  equatorial  Atlantic,  2,000 
fathoms,  making  for  the  general  mean  of  the  Atlantic, 
2,166  fathoms.§  The  mean  depth  of  the  Pacific  between 

» Herschel:  Physical  Geography,  2d  ed,  19. 

+  Haughton,  Proc.  Roy.  Soc.,  vol.  26,  p.  53, 1877. 

t  W.  B.  Carpenter,  Encyc.  Brit.,  Art.  "Atlantic  Ocean." 

§  This  was  written  before  learning  Sir  Wyville  Thomson's  estimate  as  stated 
in  his  Rede  lecture  at  Cambridge  in  1877.  He  makes  the  mean  depth  of  the  At- 
lantic about  2,500  fathoms,  and  this  opinion  is  probably  as  near  the  truth  as  we 
can  come. 


PROGRESSIVE    SUBSIDENCE    OF   TEMPERATURE.       467 

Japan  and  San  Francisco,  according  to  the  calculations  of 
the  United  States  Coast  Survey,  based  on  the  transmission 
of  an  earthquake  sea  wave,  is  2,300  fathoms.  Calling 
this  the  mean  depth  of  the  Pacific,  and  giving  the  number 
equal  weight  with  that  for  the  depth  of  the  Atlantic,  as 
found  above,  the  mean  depth  of  the  two  is  2,233  fathoms, 
or  12,398  feet,  or  2.538  miles,  which  may  be  provisionally 
assumed  as  the  mean  depth  of  the  general  ocean.  This  is 
6.8  times  as  deep  as  assumed  by  M.  Ssemann. 

(3.)  Calculation  of  absorptive  capacity  of  the  plane'.ary 
pores.  Having  the  area  and  mean  depth  of  the  ocean,  we 
may  ascertain  its  cubic  contents;  then,  knowing  the  index 
of  absorption  of  the  earth's  crust,  a  simple  application  of 
the  general  formula  before  deduced  (p.  382)  gives  the 
thickness  of  cooled  crust  requisite  to  effect  the  absorption 
of  the  ocean.  Many  circumstances  may  render  the  absorb- 
ent property  of  the  deep  crust  different  from  that  of  sur- 
face rocks.  Any  residual  heat  above  the  temperature  at 
which  experiments  have  been  made  would  probably  dimin- 
ish the  power  of  absorption.  On  the  contrary,  great  con- 
densation of  the  water  might  take  place,  either  through 
the  physical  action  of  minute  pores,  or  the  great  pressure 
of  superincumbent  matter.  In  the  present  state  of  knowl- 
edge, we  can  only  assume  that  the  absorbent  property  of 
the  crust  is  about  that  of  the  superficial  rocks.  Employ- 
ing the  index  of  absorption  given  by  Dr.  Cutting's  experi- 
ments, and  neglecting  the  superficial  zone  already  satu- 
rated with  water,  our  formula  gives  490.8  miles  as  the 
thickness  of  the  terrestrial  zone,  which  would  retire  all  the 
water  now  filling  the  ocean's  basin.  If  we  wish  to  know 
what  thickness  of  zone  below  the  zone  already  saturated 
would  suffice  to  absorb  the  ocean,  we  may  employ  first  the 
formula  given  for  obtaining  the  thickness  of  the  saturated 
zone.  In  this,  if  we  assume  the  rate  of  increase  of  tem- 
perature downward  to  be  one  degree  for  50  feet;  the 


468  PLANETARY    DECAY. 

mean  temperature  at  the  surface,  47°;  the  temperature  at 
which  water  vaporizes  in  the  crust  of  the  earth,  212° 
Fahr.,  and  the  depth  to  constant  temperature,  80  feet,  the 
saturated  zone  is  shown  to  be  8,330  feet  or  1.5776  mile. 
Employing  this  value  in  the  general  formula,  we  find  that 
a  zone  491.42  miles  thick  within  the  present  saturated  zone 
would  absorb  the  ocean's  water. 

According  to  M.  Sasmann's  calculations,  the  pores  of 
the  rocks  of  the  totally  refrigerated  earth,  after  having 
taken  in  the  waters  of  the  ocean,  would  amply  suffice  for 
the  absorption  of  the  atmosphere  also.  But  I  have  shown 
that  he  has  assumed  a  depth  for  the  ocean  which  is  over 
eight  times  too  small,  and,  on  the  contrary,  an  absorbent 
property  of  surface  rocks  which  is  ten  times  too  great. 
Accordingly,  it  does  not  appear  that  this  porosity  is  suffi- 
cient for  the  total  retirement  of  the  water  and  air. 
Taking  Sir  John  Herschel's  mass  of  the  atmosphere  (re- 
duced to  surface  density,  Y^irimrff)*  its  relative  volume  is 
.003837;  and  application  of  the  formula  adapted  to  this 
case  (p.  383,  note)  shows  that  this  is  more  than  the 
capacity  of  the  pores  would  receive  after  the  absorption 
of  the  ocean.  This  is  evident,  indeed,  from  the  fact  that 
the  ocean  would  appropriate  .3276  of  the  earth's  total 
capacity,  leaving  only  2.052  times  this  amount  unappro- 
priated, while  the  relative  volume  of  the  ocean  being 
.001409,  the  relative  volume  of  the  atmosphere  (.008837) 
is  2.723  times  that  of  the  ocean.  It  is  entirely  probable, 
however,  that  absorbed  air  would  undergo  a  sufficient  con- 
densation to  render  the  whole  atmosphere  absorbable. 
Supposing  a  somewhat  free  communication  among  the 
pores,  columns  of  air  would  exist  reaching  from  the  zone 
of  the  absorbed  water  to  the  earth's  surface,  which  would 
be  1,230  miles.  Now  the  whole  depth  of  the  atmosphere 
reduced  to  density  of  surface  air  would  be  but  five  miles. 
At  half  the  depth  of  the  zone  left  unoccupied  by  the 


PROGRESSIVE   SUBSIDENCE    OF   TEMPERATURE.       469 

ocean  —  that  is,  at  615  miles  —  there  would  exist,  making 
no  allowance  for  diminished  gravity  below  the  surface,  a 
pressure  of  123  atmospheres,  which  would  condense  the 
air  into  123  times  less  than  its  surface  volume.  If  any- 
thing should  interfere  with  the  application  of  Mariotte's 
law,  it  would  be  an  attraction  for  the  air  which  would 
produce  an  equal  or  greater  effect;  as  in  the  case  of  the 
condensive  absorption  exerted  by  charcoal,  platinum- 
sponge  and  some  meteoric  stones.  This  method  of  cal- 
culation, however,  assumes  erroneously  that  each  addi- 
tional five  miles  of  depth  adds  one  atmosphere  to  the 
pressure.  But  as  gravity  beneath  the  surface  of  the  earth 
varies  as  the  distance  from  the  centre,  the  pressure  at  the 
bottom  of  615  miles  would  be  only  104  atmospheres,  and 
at  the  depth  of  1,230  miles,  208  atmospheres.*  There  can 
be  no  doubt,  consequently,  after  this  correction,  that  the 
condensation  would  be  sufficient,  and  much  more  than 
sufficient,  to  permit  the  final  withdrawal  of  the  terrestrial 
ocean  and  atmosphere. 

As  to  the  remoteness  of  the  epoch  when  the  earth's 
water  and  atmosphere  will  have  been  absorbed,  little  can 

*Letr  be  the  earth's  radius  and  5  x  be  the  depth  beneath  the  surface,  then 
the  pressure  due  to  successive  five-mile  zones  will  be  expressed  in  terms  of  one 
atmosphere,  as  follows : 

r  —  5    r  —  5 X  2    r— 5 X  3    r  —  5 X  4  r  —  5x 

r  r  r  r  Ir      ' 

The  last  term  expresses  the  pressure  due  to  the  last  five  miles.    The  pressure 

due  to  the  middle  five  miles  is — ,  and  this  is  the  mean  pressure  in  the 

whole  series  of  zones. 

If  5  x  =  1,230  miles,  the  mid  pressure  is 

3%L73615  =  -844  atmos-  =  mean  Pressure. 

O3OO 

The  pressure  due  to  the  lowest  five-mile  zone  is 

3963  — 1230 

5j— .689  atmosphere. 

The  total  pressure  at  the  bottom  is 

lOMfl 

=g2  X  .844  =  207.624  atmospheres, 
and  the  pressure  at  the  bottom  of  a  column  half  as  high  is  half  as  great. 


470  PLANETARY    DECAY. 

be  said.  In  Mars  we  have  a  planet  whose  terrestrial 
stage,  according  to  our  theory,  would  have  been  reached 
9,500,000  years  ago,  if  we  suppose  its  incrustation  to  have 
begun  when  the  earth's  began,  and  use  the  table  of  time 
ratios  heretofore  given.  Since  that  epoch  Mars  has  con- 
tinued to  advance  in  its  evolution  at  a  rate  two  and  a  half 
times  as  rapid  as  the  earth,  and  yet  Mars  has  not  attained 
the  stage  of  complete  atmospheric  absorption.*  That  is, 
if  the  evolution  of  the  earth  can  be  compared  with  that 
of  Mars,  it  will  be  more  than  24,000,000  years  before  the 
earth's  atmosphere  is  absorbed.  And  to  this  must  be 
added  the  difference  in  age  of  the  two  planets.  On  the 
other  hand,  assuming  the  same  time  ratios  as  before,  we 
mav  reason  from  the  condition  of  the  moon,  and,  adopting 
14,000,000  years  as  the  earth's  incrusted  age,  the  moon 
reached  the  terrestrial  condition  11,666,666  years  ago. 
The  advance  of  the  moon  in  its  evolution  since  that 
epoch  is  equal  to  the  advance  to  be  made  by  the  earth  in 
70,000,000  years.  But  the  moon's  atmosphere  is  absorbed, 
and  hence  within  70,000,000  years  the  absorption  of  the 
terrestrial  atmosphere  will  be  effected.  That  is,  reasoning 
from  the  slender  data  within  reach,  the  absorption  of  the 
earth's  atmosphere  will  be  effected  in  a  period  lying 
between  24,000,000  and  70,000,000  years. 

The  secular  disappearance  of  the  surface  waters  of  the 

*  It  will  be  noticed  that  all  the  calculations  made  in  reference  to  the  absorp- 
tion of  planetary  water  and  air  assume  a  planetary  density  equal  to  the  mean 
density  of  granite  (2.625).  But  the  deeper  portion  of  the  earth  has  a  much 
higher  density,  and  hence,  probably,  possesses  a  lower  index  of  absorption,  and 
would  not,  consequently,  be  able  to  effect  all  the  absorption  attributed  to  it  in 
the  text.  Similarly,  the  moon,  though  its  density  is  only  .607  compared  with 
earth,  exceeds  granite  in  density,  and  would  have  a  lower  absorptive  capacity 
than  we  have  attributed  to  it.  Mars,  also,  with  a  mean  density  (.6481)  a  little 
greater,  is  more  dense  than  granite,  and  with  a  presumably  larger  proportion  of 
water  and  air,  might  be  supposed  incapable  of  completely  absorbing  its  surface 
fluids;  so  that,  after  all  possible  absorption  is  effected,  a  residual  portion  of 
the  Martial  atmosphere  (if  not  of  water)  will  remain  permanently.  This  con- 
sideration bears  on  the  inferior  limit  of  time  within  which  the  earth's  atmos- 
phere may  be  absorbed.  That  is,  it  may  not  be  "  more  than  24,000,000  years." 


PEOGEESSIVE   SUBSIDENCE    OF   TEMPERATURE.      471 

earth  is  a  fact  of  observation  and  record.  The  ocean  was 
once  universal;  it  is  in  our  times  withdrawn  from  three- 
tenths  of  the  earth's  surface.  This  is  generally  attributed 
to  the  progressive  increase  of  the  inequalities  of  the  ter- 
restrial surface;  and  it  is  not  possible  to  disprove  the  posi- 
tion. But  there  are  many  indications  of  a  slow  desicca- 
tion of  the  land  during  human  occupation.  Lakes  have 
disappeared  or  diminished;  marshes  and  alluvial  areas 
occupy  situations  once  water-covered.  Climates  have  be- 
come more  arid;  and  many  regions  once  productive  have 
become  sterile  and  uninhabitable.  Numerous  illustrations 
of  these  statements  are  familiar  to  every  intelligent  per- 
son. I  have  been  accustomed  for  fifteen  years  to  discuss 
the  subject  in  my  university  lectures.  No  one,  however, 
has  given  the  facts  so  much  consideration  as  Professor  J. 
D.  Whitney;  and  after  directing  the  attention  of  the 
reader  to  the  interesting  phenomenon,  I  must  refer  him  for 
the  abundant  facts,  to  Professor  Whitney's  writings.* 

To  the  present  probable  condition  of  the  moon  I  have 
had  frequent  occasion  to  allude.  That  its  surface  is  desti- 
tute of  air  and  water  is  generally  admitted.  M.  Faye  main- 
tains that  these  fluids  were  never  present;  but  it  is  impos- 
sible to  adopt  any  theory  of  the  origin  of  the  moon  by 
derivation  from  the  earth  or  from  a  common  mass  with  the 
earth,  and  deny  the  necessity  of  aqueous  and  atmospheric 

*  J.  D.  Whitney:  American  Naturalist,  x.  513,  September,  1876;  Memoirs, 
Museum  of  Comparative  Zoology,  Cambridge,  Vol.  vii,  On  Climatic  Changes  of 
Later  Geological  rimes.  Part  I,  120  pp.,  1880;  Part  II,  121-264  pp.,  1882,  Part  III, 
265-394  pp.,  1883.  See  also  Amer.Jour.  ScL,  III,  xx,  460,  xxiii,  489-90,  xxv,  153. 
For  some  shrinkages  of  American  lakes,  see  King:  Geology  of  the  Mh  Paral- 
lel, i,  490-504;  Stevenson,  in  Wheeler's  Report,  iii,  453-71;  Howell,  ib.,  250-1; 
Hayden,  Report  on  Wyoming,  1870,  72-3  and  Annual  Report  for  1874,  48;  Pacific 
R.  R.  Report,  ii,  97;  Endlich,  Hayden  Report,  1875,  147-8;  Nature,  xxii,  41;  A. 
R.  C.  Selwyn:  Geol.  of  Canada,  1873-4,  27,  58;  C.  Robb:  Geol.  of  Canada,  1874-5, 
53-6.  Compare  also,  A.  Winehell,  Trans.  Mich.  Agric.  See,,  1865;  Syllabus  of  a 
Course  of  Lectures  on  Geology,  1869,  7,  ib..  1870,  12;  ib.,  1874,  20,  24;  ib.,  1879,  44, 
112;  Amer.  Jour.  Scl.,  II,  xxxviii,  November,  1864;  Sketches  of  Creation,  1870, 
237-9. 


472  PLANETARY    DECAY. 

constituents.    The  apparent  absence  of  such  fluids  can  only 
be  explained  on  the  theory  of  their  complete  absorption. 

By  the  logic  of  our  theory  we  are  constrained  to  believe 
that  water  and  air  have  disappeared  from  the  surface  of 
every  body  in  our  system,  of  greater  age  than  the  moon, 
and  not  much  surpassing  it  in  size,  provided  its  solids  and 
liquids  were  originally  proportioned  somewhat  as  in  the 
moon  and  earth.  But  according  to  our  theory  also,  all 
the  older  bodies  must  have  received  a  larger  proportion  of 
fluids  than  the  earth.  The  water  surface  of  Mars  must 
have  been  in  larger  ratio  than  on  the  earth,  and  the  Mar- 
tial atmosphere  must  have  been  more  voluminous.  Then, 
perhaps,  Mars  might  become  completely  refrigerated  with- 
out absorbing  all  its  water.  Still  more  likely,  a  surplus  of 
atmosphere  would  remain.  That  a  full  supply  of  water 
and  air  is  not  present  is  manifest  from  the  comparatively 
unclouded  condition  of  the  disc  of  the  planet.  In  this 
view,  the  indications  of  an  atmosphere  will  never  disap- 
pear from  Mars.  It  may  have  been  senescent  and  refrig- 
erated for  millions  of  years  —  as  indeed  our  moon  may 
have  been.  As  to  the  Martial  satellites,  it  cannot  be 
doubted  that  they  have  long  since  attained  their  final  con- 
dition, so  far  as  concerns  heat  and  absorption  of  fluids; 
and  that  cannot  be  far  different  from  the  condition  of 
their  primary. 

The  asteroids  should  present  a  still  further  divergence 
from  the  conditions  of  the  earth.  They  are  probably  ice- 
covered  and  frozen  to  the  core,  each  retaining  an  abundant 
quota  of  atmosphere. 

Jupiter,  I  have  assumed,  in  consequence  of  his  enor- 
mous mass,  to  be  still  far  short  of  the  terrestrial  stage. 
The  large  percentage  of  fluids  in  his  constitution  renders 
it  improbable  that  any  considerable  land  surface  should 
ever  emerge;  and  still  more  improbable  that  the  fluids 
should  ever  become  completely  absorbed.  Jupiter's  glacier- 


SYNCHRONISTIC  MOTIONS  AND  TIDAL  FINALITIES.  473 

clad  satellites  present  the  picture  of  Jupiter's  remote  future 
destiny. 

In  the  ultra-Jovian  planets  this  destiny  is  attained.  All 
fluid  absorption  of  which  they  are  susceptible  is  a  finality 
long  since  attained  in  each  of  the  three  successively.  They 
are  globes  of  solid  ice,  inclosing  cores  of  rocky  material,  and 
wrapped  in  vapor-laden  atmospheres.  (See  chapter  iii,  §  6.) 

Looking  in  the  other  direction,  it  may  be  suggested 
that  Venus  and  Mercury,  in  consequence  of  their  dimin- 
ished proportion  of  fluids,  will  become  desiccated  and  air- 
less at  a  relatively  earlier  age  than  the  earth.  That  they 
are  not  yet  so  is  indicated  by  the  envelopes  of  vapor  which 
conceal  their  discs  from  view. 

§-3.   SYNCHRONISTIC  MOTIONS  AND  TIDAL  FINALITIES. 

It  appears  that  tidal  influences  have  performed  a  part 
of  prime  importance  in  the  evolution  of  worlds.  I  have 
had  former  occasion  to  explain  these  influences  upon  the 
rotation  of  cosmic  bodies,  and  have  pointed  out  the  tidal 
interactions  of  the  earth  and  moon  and  of  the  sun  and 
planets.  The  subject  comes  again  into  view  in  connection 
with  the  ulterior  vicissitudes  of  planetary  bodies  which  we 
are  now  grouping  in  a  connected  presentation. 

Directing  our  attention  first  to  the  interactions  in  which 
the  earth  is  concerned,  we  perceive  that  the  tidal  retarda- 
tion which  it  is  destined  to  experience  will  first  bring 
about  synchronism  between  the  day  and  the  lunation. 
The  earth  and  moon  will  turn  permanently  the  same  sides 
toward  each  other,  and  the  two  will  rotate  as  parts  of  a 
rigid  system  about  a  common  axis.  The  reaction  of  the 
earth  upon  the  moon  will  have  caused  it  to  recede  to  the 
distance  of  about  347,100  miles,  and  the  lunation  will, 
accordingly,  have  been  lengthened  to  48.36  days.* 

*Thomson  and  Tail :  Treatise  on  Natural  Philosophy,  2d  ed.  §  276.  The  tidal 
retardation  of  the  earth's  rotation  was  first  suggested  hy  Kant,  in  1754. 


474  PLANETARY    DECAY. 

The  tidal  retardation  of  the  earth's  rotation,  that  is, 
the  gradual  lengthening  of  the  day,  is  a  fact  of  observa- 
tion. The  number  of  seconds  since  the  occurrence  of  an 
ancient  eclipse,  for  instance,  would  be  somewhat  less  than 
calculation  shows,  if  the  day,  and  hence  the  second,  has 
been  slowly  lengthened.  The  subject  was  investigated  by 
Laplace,  on  the  basis  of  eclipse  observations  recorded  by 
Hipparchus,  720  B.C.,  and  shows  that  the  length  of  the 
day  had  not  increased  one  ten-millionth  of  itself,  or  jfa  of 
a  second,  in  the  intervening  time.  But  Adams,  in  1859, 
pointed  out  an  oversight  in  the  investigation  of  Laplace 
on  the  acceleration  of  the  moon's  mean  motion,  showing 
that  one-half  of  its  apparent  acceleration,  relatively  to 
the  angular  velocity  of  the  earth's  rotation,  remained  un- 
explained. That  is,  the  moon  was  5". 7  in  advance  of  the 
position  she  would  have  relatively  to  a  meridian  on  the 
earth  at  the  end  of  a  century,  after  all  known  disturbing 
causes  had  been  taken  into  account.  This  is  the  same  in 
effect  as  if  the  earth  in  her  rotary  motion  were  a  little  be- 
hind, and  Delaunay  soon  showed  that  this  was  probably 
the  true  explanation.  Investigating  the  amount  of  tidal 
retardation  of  the  earth's  axial  velocity  due  to  the  influence 
of  both  sun  and  moon,  and  allowing  for  the  retardation  of 
the  moon  by  reaction  of  the  lunar  tide,  he  found  that  the 
earth's  meridian  was  behind  the  position  required  by  the 
lunar  motion,  by  just  about  the  amount  of  the  tidal  retard- 
ation. Thus  it  appears  that  the  terrestial  day  is  shortened 
about  twenty-two  seconds  in  a  century,  and  tidal  action 
is  the  cause.*  Should  this  rate  of  retardation  continue,  and 
should  the  length  of  a  lunation  not  change,  a  state  of  syn- 
chronism would  be  attained  in  about  378,000  years.  But 
the  rate  will  be  diminished,  both  by  the  slow  recession  of 
the  moon  and  by  the  growing-  infrequency  of  the  tide. 

*But  on  the  contrary,  see  E.  J.  Stone,  Proc.  Roy.  Soc.,  Apr.  12, 1883,  Nature, 
xxviii,  71. 


SYNCHRONISTIC  MOTIONS  AND  TIDAL  FINALITIES.  475 

The  length  of  the  lunation  will  also  be  gradually  in- 
creased. 

After  a  state  of  lunar-terrestrial  synchronism  shall  have 
been  attained,  it  cannot  remain  undisturbed  through  the  in- 
definite future.  The  solar  tide  still  exists,  though  it  recurs 
only  once  in  forty-eight  days,  with  the  antitide  intervening. 
This  tide  also  lags,  and  the  sun's  action  upon  it  yields  a  tan- 
gential component  against  the  rotation  of  the  earth,  tend- 
ing to  reduce  the  earth's  rotary  motion  below  the  rate  of 
the  moon's  orbital  motion.  That  is,  in  course  of  time,  the 
lunar  tide,  instead  of  being  ahead  of  the  moon's  posi- 
tion, will  be  behind  it,  and  the  moon  and  sun  will  contend 
for  the  control  of  the  earth's  rotation.  The  sun  will  strive 
to  lengthen  the  day  and  the  moon  will  now  strive  to  shorten 
it.  The  reaction  of  the  lunar  tide  will  now  retard  the 
moon's  motion,  and  centripetal  force  will  gain  a  slight 
ascendancy.  As  a  consequence,  the  moon  will  approach 
the  earth  and  will  ultimately  be  precipitated  upon  it. 

Meantime,  the  tidal  interactions  between  the  earth  and 
sun  repeat  those  between  the  moon  and  earth.  The  lag- 
ging of  the  terrestrial  tide  on  the  sun,  acted  on  by  the 
earth,  tends  to  equalize  the  sun's  rotation  and  the  earth's 
revolution.  The  reaction  of  this  tide  on  the  earth's  motion 
increases  the  distance  between  the  earth  and  sun,  and  the 
lagging  solar  tide  on  the  earth,  acted  on  by  the  sun,  con- 
tinually diminishes  the  rotary  velocity  of  the  earth,  and 
(through  the  displacement  of  the  lunar  tidal  protuberance) 
the  orbital  velocity  of  the  moon,  thus  accelerating  the 
precipitation  of  the  moon  on  the  earth.  As  an  outcome 
of  this  contest  between  the  moon  and  sun,  if  I  reason 
correctlv,  the  day  will  become  a  little  longer  than  the 
lunation,  so  that  the  lunar  tidal  protuberance  will  exist 
continually  a  little  behind  the  moon's  position,  and  the 
solar  tidal  protuberance  a  little  ahead  of  the  sun's  posi- 
tion, so  placed  that  the  accelerating  influence  of  the  moon 


476  PLANETARY    DECAY. 

will  be  exactly  balanced  by  the  retarding  influence  of  the 
sun.  Thus  the  moon  will  perpetually  approach  the  earth, 
and  the  earth  will  perpetually  recede  from  the  sun.  But 
when  eventually  the  moon  falls  to  the  earth,  the  solar  tide 
will  bring  the  latter  to  such  a  rate  of  rotation  that  the 
day  will  equal  the  (lengthened)  year;  and  with  no  further 
interferences,  this  state  of  rotation  would  continue  forever. 

If  we  consider  the  ultimate  tidal  history  of  Venus,  it  is 
manifest,  on  grounds  before  explained,  that  so  long  as 
fluids  exist  on  the  surface  of  the  planet,  or  so  long  as  a 
state  of  incomplete  rigidity  remains,  a  solar  tide  will  exist, 
whose  lagging  must  furnish  the  condition  of  a  tangential 
component  opposing  axial  rotation.  Venus  will  therefore 
be  reduced  to  a  state  of  synchronism,  and  will  revolve  at 
an  increased  distance  from  the  sun.  Simultaneously  the 
tide  raised  on  the  solar  surface  will  offer  the  conditions  of 
solar  rotary  retardation,  and  neglecting  the  influence  of 
other  planets,  Venus  and  the  sun  will  finally  rotate  as  a 
rigid  system  around  their  common  centre  of  inertia.  The 
tidal  influence  of  Venus  upon  the  sun  is  two  and  a  third 
times  as  great  as  that  of  the  earth;  hence  the  sun  will  obey 
Venus  at  first,  and  arrive  at  synchronism  with  that  planet. 
Then,  as  the  rotary  velocity  of  Sun-Venus  will  exceed  the 
orbital  velocity  of  the  earth,  the  geal  tide  raised  on  the 
sun  will  be  in  advance  of  the  line  joining  the  centres  of 
the  earth  and  sun,  so  that  the  tangential  component  of  the 
earth's  action  on  the  solar  geal  tide  will  be  retardative, 
and  the  sun  will  tend  toward  synchronism  with  the  earth. 
The  sun's  tidal  reaction  on  Venus  will  now  be  retardative 
and  Venus  will  approach  the  sun.  The  remote  tidal  inter- 
action with  Mercury  will  be  similar.  It  may  be  noted  also 
that  the  tidal  control  exerted  by  that  planet  over  the  rota- 
tion of  the  sun  will  be  to  that  exerted  by  the  earth  as 
1.118  to  1. 

There  is  ground  for  believing  that  the  rotary  motions 


INFLUENCE   OF   INTERPLANETARY    RESISTANCES.    477 

of  all  the  satellites  of  our  system  have  long  since  become 
synchronistic  with  their  orbital  motions.  In  a  system  em- 
bracing numerous  moons,  like  Jupiter's,  each  satellite  pro- 
duces its  separate  and  independent  effect,  and  these  are 
always  concurrently  retardative.  In  some  distant  age  the 
rotation  of  the  planet  will  become  coincident  with  the 
revolution  of  the  nearest  satellite.  The  retardative  action 
of  this  will  then  cease,  and  the  retardation  will  continue 
under  the  influence  of  the  other  satellites,  toward  the  at- 
tainment of  synchronism  with  the  second  satellite.  But 
meantime  the  first  satellite  has  a  greater  angular  velocity 
than  the  planet,  and  the  relation  of  Phobos  to  Mars  is 
realized.  It  tends  now  to  accelerate  the  rotation  of  the 
planet.  The  reaction  of  the  planetary  tide  on  this  sat- 
ellite retards  its  motion,  and  brings  it  on  a  course  of  pre- 
cipitation in  a  spiral  path  upon  the  planet.  At  length 
synchronism  with  the  second  satellite  is  attained,  and  its 
history  repeats  the  history  of  the  first.  Ultimately,  all  the 
satellites  except  the  last  are  precipitated  on  the  primary, 
and  the  planet's  rotation  attains  synchronism  with  its 
revolution.  Theoretically  the  sun  must  be  viewed  as  still 
further  retarding  the  planet's  rotation  by  action  on  the 
lagging  solar  tide;  and  this  tide  reacting  on  the  last  satel- 
lite, retards  it  and  accomplishes  precipitation  on  the  planet. 
Finally,  disregarding  the  presence  of  other  planets,  this 
planet  and  the  sun  attain  synchronistic  motions,  as  in  the 
case  of  the  earth-sun.  The  tidal  action  of  the  sun,  how- 
ever, upon  the  major  planets  is  so  slight  relatively  that  the 
events  contemplated  are  removed  to  a  future  excessively 
remote,  and  we  may  fairly  expect  them  to  be  forestalled 
by  other  eventualities. 

§  4.   ULTIMATE   INFLUENCE   OF  INTERPLANETARY  RE- 
SISTANCES. 

The  analogies  of  nature  and  the  ascertained  facts  of  physical  science  for- 
bid us  to  doubt  that  every  one  of  them  — every  star  and  every  body  of  every 


478  PLANETARY    DECAY. 

kind,  moving  in  any  part  of  space  — has  its  relative  motion  impeded  by  the 
air,  gas,  vapor,  medium,  or  whatever  we  choose  to  call  the  substance  occupying 
the  space  immediately  round  it.— SIB  W.  THOMSON  and  P.  G.  TAIT. 

It  is  a  common  remark  that  Laplace  found  the  harmony 
of  the  solar  system  stable,  provided  that  interplanetary 
space  is  a  vacuum,  and  the  planets  themselves  are  per- 
fectly rigid  bodies.  More  recent  science  has  shown  that 
neither  of  these  conditions  of  indefinite  stability  exists. 
Occasions  have  arisen  in  other  connections,  to  point  out 
many  of  the  facts  which  contravene  the  conditions  of 
stability,  but  it  will  be  useful  to  summarize  in  due  connec- 
tion the  indications  of  eventual  conglomeration  around 
centres  of  orbital  motion.  Were  the  planets  all  as  solid 
as  granite,  there  would  exist  sufficient  plasticity  to  yield 
a  tidal  protuberance  under  their  mutual  actions  and  that 
of  the  sun.  It  was  shown  in  the  last  section  that  tidal 
actions  and  interactions  affect  both  rotary  and  orbital  mo- 
tions; and  that  under  certain  circumstances,  mere  tides 
tend  to  precipitate  planetary  masses  upon  their  centres  of 
motion.  The  freer  the  mobility  of  certain  parts  of  a  tide- 
bearing  body,  the  more  efficient  this  action,  provided  some 
of  the  other  parts  are  relatively  much  more  rigid,  to  fur- 
nish points  of  resistance  to  the  parts  tidally  moved.  But 
probably  no  matter  exists  so  completely  rigid  as  not  to 
undergo  relative  displacement  in  the  presence  of  the  tre- 
mendous forces  exerted  by  planetary  and  solar  masses. 
Hence,  on  planets  not  covered  by  waters,  and  on  planets 
whose  seas  have  been  converted  into  ice,  tidal  action  con- 
tinues, and  tidal  finalities  are  impending.  Such  results 
flow  from  the  absence  of  complete  planetary  rigidity. 

A  more  commonly  recognized  cause  of  a  tendency 
toward  central  precipitation  is  the  presence  of  resisting  or 
colliding  matter  in  the  interplanetary  spaces.  In  another 
connection  *  I  have  discussed  the  diffusion  of  meteoroidal 

*  Especially  in  Part  I,  ch.  i,  §  6. 


INFLUENCE    OF   INTERPLANETARY    RESISTANCES.    479 

matters  and  of  other  possible  forms  of  matter  consisting  of 
gases,  vapors  or  ethers,  and  have  reached  the  conclusion 
that  space  is  so  far  from  the  condition  of  a  vacuum  that  it 
seems  rather  to  be  a  plenum,  the  contents  of  which  neces- 
sarily interfere  with  all  relative  motions  in  the  universe. 
The  conception  of  an  extremely  attenuated  material  me- 
dium has  been  entertained  ever  since  the  time  of  Sir  Isaac 
Newton,  and  many  eminent  authorities  have  felt  great 
confidence  in  its  reality,  and  have  discussed  its  necessary 
properties —  sometimes  holding  it  to  be  a  continuous  fluid, 
and  in  other  cases  considering  it  rather  to  have  an  atomic 
or  discrete  constitution.*  It  is  impossible  that  an  ethereal 
medium,  however  tenuous,  should  exist  without  impressing 
results  on  the  motions  of  cosmical  bodies.  This  influence 
has  been  thought  detected  in  the  accelerated  angular 
velocities  of  Encke's  and  Winnecke's  comets,  particularly 
the  former,  which  moves  throughout  its  whole  course  in 
an  orbit  relatively  not  remote  from  the  sun.  The  ethereal 
medium  is  generally  assumed  to  diminish  in  intensity  with 
increase  of  distance  from  the  sun.  The  assumption  that 
the  density  varies  inversely  as  the  square  of  the  distance 
agrees  best  with  observation  on  the  cometary  effects  of 
supposed  ethereal  action.  The  formula?  expressing  these 
perturbative  effects  show  that  the  tendency  of  the  medium, 
conjointly  with  solar  attraction,  would  be  to  continually 
accelerate  the  mean  motion  and  diminish  the  eccentricity 
of  the  orbit.  Accelerated  motion  arises  from  diminished 
distance  from  the  sun.  If  these  conclusions  are  correctly 
based,  we  are  therefore  enabled  to  make  actual  observa- 
tion of  the  slow  spiral  approach  of  a  body  toward  its  cen- 
tre of  motion.  It  must  be  said,  however,  that  the  later 
movements  of  Encke's  comet  do  not  clearly  sustain  the 
theory  of  slow  precipitation,  and  some  high  physical  au- 

*  We  might  add  to  the  citations  heretefore  made  (p.  52)  Kretz:  Matttre  et 
Ether;  indication  cPvne  methode  pour  ttablir  les  proprietes  de  V  Ether. 


480  PLANETAEY    DECAY. 

thorities  deny  that  its  entire  observed  history  favors  the 
doctrine  of  precipitation,  or  lends  any  distinct  evidence  of 
the  existence  of  a  resisting  medium.*  If,  however,  the 
earlier  and  later  observed  movements  reveal  irregulari- 
ties in  the  motion  of  the  comet  which  cannot  be  ascribed 
to  planetary  perturbations,  it  is  allowable  to  suspect  that 
the  temporary  and  unknown  cause  of  irregularities  will 
hereafter  cease  to  act,  and  the  subsequent  accelerated 
motion  of  the  comet  reveal  with  increased  distinctness  the 
presence  of  a  resisting  medium.  But  whether  human  skill, 
in  the  course  of  one  or  two  generations,  shall  succeed  or 
not  in  discovering  the  effects  of  a  resisting  medium,  we 
must  admit  that  the  effects  are  real,  or  incur  all  the 
embarrassment  of  ignoring  the  existence  of  any  vibratory 
medium  for  transmitting  the  radiations  of  the  sun  and 
other  heavenly  bodies.  If  we  admit,  even  in  theory,  the 
existence  of  a  universal  material  fluid,  we  must  admit,  as 
a  consequence,  the  ultimate  precipitation  of  the  planetary 
bodies  upon  their  centres  of  motion. 

I  have  heretofore  expressed  the  opinion  that  another 
cause  exists  in  space  adequate  to  exert  the  resisting  action 
generally  ascribed  to  the  ethereal  medium.  That  cause  is 
meteoroidal.  It  is  easy  to  conceive  that  a  perturbation 
proceeding  from  this  cause  would  produce  a  mean  effect 
equivalent  to  that  of  a  resisting  force  acting  in  the  tan- 
gent to  the  instantaneous  orbit;  and  that  the  amount  of 
the  perturbation  or  resistance  should  increase  as  the  dis- 
tance from  the  sun  diminishes.  It  seems  to  me  that  a 
disturbance  of  this  nature  is  more  clearlv  established  than 
the  resisting  property  of  the  ethereal  fluid. 

*  Dr.  Backluud,  of  Pulkowa,  concludes  from  an  investigation  of  the  motion 
of  Encke's  comet  that  "  if  there  exists  a  tangential  force  which  varies  with  the 
dimensions  of  the  comet's  orbit,  its  effect  is  not  only  secular  but  periodic." 
His  investigation  proves  that  the  acceleration  of  the  mean  motion  in  tin-  period 
1871-81  was  less  than  half  the  value  found  by  Kncke  and  Asten  for  the  period 
1819-65  (Nature,  xxviii,  181).  This  is  the  latest  announcement  on  the  subject. 


INFLUENCE   OF   INTERPLANETARY    RESISTANCES.    481 

Many  trains  of  investigation  lead  toward  the  convic- 
tion that  space  is  pervaded  by  some  condition  of  matter 
in  a  state  of  general  dissemination.  The  intimation  has 
recently  come  to  us  through  the  researches  of  Captain 
Abney,  that  the  vapor  of  water  and  hydrocarbon  com- 
pounds are  possessed  of  a  general  distribution.  The 
latter,  at  least,  had  been  already  detected  in  comets  and 
in  meteoric  stones.  It  is  equally  probable  that  hydrogen 
helps  to  fill  the  void  between  us  and  the  sun;  and  no 
improbability  is  apparent  that  the  very  atmosphere  which 
we  breathe  stretches  on  indefinitely  toward  the  stars, 
diminishing  ever  in  density  as  we  recede  from  the  earth, 
but  increasing  in  density  as  we  approach  other  bodies, 
and  constituting  an  intelligible  material  intermedium. 
One  can  imagine  what  extreme  tenuity  such  a  medium 
must  possess  in  the  interplanetary  spaces  when  it  is  con- 
sidered that  the  meteoroids  moving  through  it  at  the  rate  of 
forty  miles  a  second  do  not  develop  heat  more  rapidly  than 
the  power  of  radiation  in  the  regions  which  they  traverse 
is  capable  of  conveying  it  away. 

By  some  cause  acting  after  the  manner  of  a  resisting 
medium  certain  comets  seem  to  have  been  impressed.  By 
such  a  cause  the  satellite  Phobos  may  have  been  im- 
pressed, for  it  appears  to  be  in  actual  course  of  precipita- 
tion. By  some  similar  cause  or  causes  all  the  planets 
and  satellites  must  be  slowly  affected;  and  our  inability 
to  discern  and  measure  the  results  may  be  well  ascribed 
to  their  minuteness  within  human  periods,  and  the  effect 
of  other  perturbative  causes  in  disguising  them.  It  ap- 
pears to  be  generally  admitted  that  precipitative  tenden- 
cies exist,  and  none  of  the  eventualities  of  the  distant 
future  will  be  able  to  annul  them.  We  therefore  conceive 
of  the  ultimate  return  of  the  various  members  of  the 
sun's  family  back  to  the  central  mass  from  which  they 
originally  sprang. 
31 


482  PLAKETAKY    DECAY. 

We  observe  in  the  Solar  System  a  mode  of  action 
which  in  principle  is  the  same  as  that  of  interplanetary 
matter;  but  the  action  is  exerted  by  matter  which  consti- 
tutes a  part  of  the  aggregation  acted  upon.  It  exists  in 
cometary  and  meteoroidal  trains,  in  the  rings  of  Saturn, 
and  probably  in  the  zodiacal  light  —  possibly,  also,  in  the 
swarm  of  asteroids  and  in  other  groupings  of  cosmical 
particles  and  masses.  It  is  not  conceivable  that  the  parts 
which  constitute  the  head  or  even  the  tail  of  a  comet,  for 
instance,  stones,  grains,  dust,  vapors,  move  with  such  uni- 
form velocities  and  directions  as  not  to  collide  with  each 
other.  I  have  heretofore,  following  Sir  William  Thom- 
son, ascribed  the  evidences  of  a  gaseous  glow  in  the  head 
of  a  comet  to  the  collisions  of  the  stony  constituents  of 
which  it  is  composed.  Where  mean  velocities  are  fifty  or 
one  hundred  miles  a  second,  it  requires  but  slight  differ- 
ences of  velocity  to  produce  relative  velocities  equal  to 
those  of  military  projectiles.  A  cannon  ball  moves  1,400 
to  2,000  feet  in  a  second,  and  yet  its  impact  upon  a  solid 
body  always  develops  a  flash  of  light.  But  this  velocity 
is  mere  rest  when  compared  with  that  of  a  comet  in  its 
flight.  Now,  in  case  of  these  mutual  collisions  among 
the  parts  of  a  comet,  the  velocities  of  some  will  be  accel- 
erated and  those  of  others  retarded.  Those  retarded  are 
liable,  of  course,  to  be  accelerated  again  by  other  colli- 
sions, so  that  the  total  amount  of  motion  in  the  assem- 
blage should  remain  constant,  so  far  as  actions  in  the 
system  are  concerned.  Nevertheless,  the  changed  velocity 
of  a  part  results  in  a  changed  intensity  of  action  from 
without.  Retardation  results  in  an  increase  of  centrip- 
etal tendency,  while  acceleration  results  in  an  increase  of 
centrifugal  tendency.  The  accelerated  and  retarded  parts, 
therefore,  tend  to  separate  from  each  other,  and  thus 
coming  into  changed  relations  to  an  external  action,  are 
further  separated.  In  the  nearer  proximity  of  a  great 


INFLUENCE   OF  INTERPLANETARY  RESISTANCES.    483 

attractive  mass,  as  when  a  comet  passes  near  a  planet, 
these  changed  relative  distances  of  the  cometary  parts 
from  the  mass  enable  the  latter  to  wrench  the  comet's 
constitution  to  a  destructive  extent.  The  effect  is  an 
incipient  disintegration  —  a  dispersion  of  the  parts  and 
the  commencement  of  their  precipitation  upon  the  dis- 
turbing body.  The  meteoroidal  stage  of  a  comet's  life 
exemplifies  the  progress  of  the  disintegration;  and  the 
meteoroidal  swarm  itself  must  be  regarded  as  going  to 
pieces  through  the  continuance  of  these  internal  and 
external  actions. 

As  the  rings  of  Saturn  are  probably  mere  cosmical 
atoms,  quite  as  hard  and  discrete  as  those  existing  in 
comets  and  meteoroidal  swarms,  there  is  equal  reason  to 
suppose  them  also  subject  to  mutual  collisions.  In  such 
case,  the  parts  suffering  retardation  would  approach  the 
planet  and  circulate  with  restored  and  even  increased 
velocity,  in  nearer  proximity  to  it.  Thus  certain  particles 
of  the  Saturnian  rings  should  continually  transfer  them- 
selves from  other  regions  to  the  inner  margin  of  the  ring 
system.  The  ring  system  should  slowly,  molecularly,  grow 
inward  and  should  ultimately  come  into  contact  with  the 
planet.  Now  it  is  interesting  to  know  that  Otto  Struve, 
in  1851,  arrived  at  the  identical  conclusion  that  "the  inner 
edge  of  the  Saturnian  ring  was  gradually  approaching  the 
planet,  the  whole  ring  spreading  inward,  and  making  the 
central  opening  smaller."  This  conclusion  was  based  on 
the  descriptions  and  drawings  of  astronomers  of  the  sev- 
enteenth century,  arid  especially  of  Huygens.* 

*  Struve,  however,  has  lately  reported  the  results  of  new  measurements  made 
in  1832,  from  which  it  appears  that  the  inner  diameter  of  the  ring  though  slightly 
shorter  than  in  1851,  is  less  shortened  than  his  theory  requires.  The  space,  how- 
ever, which  in  1851  separated  the  inner  or  dark  ring  from  the  bright  one  is  now 
closed  up,  and  the  dark  ring  seems  to  be  merely  a  faint  continuation  of  the 
bright  ring.— Astron.  Nachrichttn,  No.  2948.  On  these  rings  I  cite  further,  G. 
A.  Hirn:  JUemoire  sur  les  conditions  cTtquilibre  et  sur  la  nature  probable  det 
anneaux  de  Saturn,  1872;  and  Le  Monde  de  Saturn,  ses  condition*  ^existence  et 
de  duree,  1872. 


484  PLANETAKY   DECAY. 

If  the  "  zodiacal  light,"  as  commonly  supposed,  is  caused 
by  sunlight  reflected  from  an  assemblage  consisting  of 
myriads  of  solid  masses  of  matter,  then  a  similar  action 
must  take  place  among  them,  and  the  assemblage  must 
gradually  spread  itself  in  the  plane  of  its  orbit  toward  the 
sun.  These  interactions  would  thus  conspire  with  the 
actions  of  other  interplanetary  matter  in  supplying  a  con- 
tinuous descent  of  meteoroidal  substances  upon  the  body 
of  the  sun. 

If  the  asteroidal  group  is,  as  some  suppose,  sufficiently 
numerous  to  create  the  probability  of  frequent  collisions, 
then  the  slow  extension  of  this  group  sunward  over  the 
plane  of  the  mean  orbit  is  a  contingency  not  to  be  over- 
looked. 

§  5.  GENERAL  REFRIGERATION. 

1.  Planetary  Refrigeration. —  This  is  also  one  of  the 
eventualities  of  a  planet's    lifetime,  and    one    which   has 
again  and  again  been  brought  before  our  attention.     We 
see  this  state  exemplified  in  the  condition  of  our  satellite, 
and  we  believe  it  has  been  attained  in  the   satellites  of 
other  planets,  and  even  the  older  of   the  planets  them- 
selves.    We  have  traced  the  slow  processes  of  planetary 
desiccation  and   atmospheric   absorption  in  those  planets 
which  belong  to  the  earth  group,  and  have  discovered  the 
cause  of  the  perpetual  presence  of  watery  vapor  and  an 
atmosphere  in  other  planets  probably  long  since  frozen  to 
the  core.      We  recognize   the    refrigerated   state   as  an 
ulterior  stage  in  all  planetary  life. 

2.  Solar  Refrigeration. —  But  it  may  not  be  fully  ap- 
preciated that,  as  the  bodies  now  planets  were  once  suns, 
so  the  bodies  now  suns  are  destined  to  be  planets.     Even 
the  long-enduring  sun  of  our  system  is  destined  to  be  ex- 
Jiausted.     I  entertain  the   opinion  that  most  of  the  heat 
by  which  the  sun  now  maintains  the  activities  of  his  em- 


GENERAL   REFRIGERATION.  485 

pire  is  a  portion  of  the  primordial  heat  evolved  in  the 
original  aggregation  of  nebular  masses  and  their  progres- 
sive condensation.  Much  heat,  undoubtedly,  has  been 
evolved  by  later  contraction  during-  the  periods  of  plane- 
tary history.  This  process  has  greatly  retarded  the  lower- 
ing of  the  solar  temperature.  But  the  sun  has  always 
been  cooling,  and  the  reason  why  his  temperature  is  still 
so  high  is  simply  the  vastness  of  his  mass.  Whatever  ac- 
cessions of  heat  may  arise  from  further  contraction,  or 
from  meteoric  or  planetary  precipitations,  will  serve  only 
to  eke  out  the  original  supply.  These  are  indeed  neces- 
sary inferences  from  the  cosmic  theory  set  forth  in  the 
present  volume  ;  but  they  are  also  conclusions  from  inde- 
pendent considerations.  Let  us  glance  at  some  of  the  data. 

(1.)  Inductive  Evidences  of  Secular  Lowering  of  Ter- 
restrial and  Solar  Temperatures. —  (a)  In  Historic  Times. 
— Very  much  discussion  has  taken  place  on  the  question 
whether  human  observations  have  established  any  changes 
in  the  mean  temperature  of  terrestrial  climates.  It  is  not 
necessary  here  to  cite  the  various  facts  and  opinions,  but 
it  is  important  to  reproduce  the.  conclusion  reached  by 
Professor  J.  D.  Whitney,  who  has  given  the  whole  subject 
a  thorough  and  patient  examination.*  He  says:  "There 
is  evidence  very  considerable  in  amount  and  importance, 
to  the  effect  that  a  decrease  in  temperature  during  historic 
times  has  manifested  itself  in  various  ways  besides  desic- 
cation." 

(&)  In  Prehistoric  Times  —  No  aspect  of  the  palseon- 
tological  relics  of  former  periods  is  less  questionable  than 
their  testimony  to  the  secular  abatement  of  terrestrial 
temperature.  It  is  not  necessary  here  to  make  particular 
citations  of  facts,  since  they  are  recorded  in  all  manuals 

*  J.  D.  Whitney :  The  Climatic  Changes  of  Later  Geological  Times,  4to., 
394pp.,  especially  219-41.  From  the  Memoirs  of  the  Museum  of  Comparative 
Zoology,  Cambridge,  Vol.  vii.  See,  also,  C.  Konig,  Kosmos,  viii,  283-91. 


486  PLANETARY    DECAY. 

of  geological  science.  The  plants,  especially,  which 
clothed  the  lands  of  the  temperate  and  arctic  zones  in 
earlier  times,  find  their  modern  allies  in  forms  restricted 
to  warmer  climates  and  to  lower  latitudes  than  their  pro- 
totypes.* The  evidences,  also,  of  a  persistent  process  of 
desiccation  of  the  continents  during  Post-Tertiary  time,  so 
industriously  accumulated  by  Professor  Whitney,  f  strongly 
sustain  the  inference  based  on  the  history  of  organic  life, 
(c)  Cause  of  Secular  Deterioration  of  Climates. —  This 
conclusion  being  admitted,  the  most  probable  explanation 
might  seem  to  be  the  progressive  cooling  of  the  earth. 
This  is  the  explanation  generally  offered  by  geologists. 
There  must,  assuredly,  have  been  an  age  when  the  surface 
temperature  of  our  planet  was  largely  influenced  by  the 
excessive  heat  of  the  interior.  It  is  not  easy  to  doubt 
that  this  influence  must  have  been  experienced  to  some 
extent,  during  the  earlier  periods  of  organic  life.  Still,  the 
present  influence  of  the  interior  is  practically  nil ;  and  in- 
vestigation shows  that  a  crust  of  very  moderate  thickness 
would  not  transmit  sufficient  warmth  to  affect  the  surface 
to  any  important  extent.  "Ten,  twenty,  thirty  times  the 
present  rate  of  augmentation  downward,"  says  Sir  Will- 
iam Thomson, J  "  could  not  raise  the  surface  temperature 
of  the  earth,  and  air  in  contact  with  it,  by  more  than  a 
small  fraction  of  a  degree  Fahrenheit.  The  earth  might 
be  a  globe  of  white-hot  iron  covered  with  a  crust  of  rock 
2,000  feet,  or  there  might  be  an  ice-cold  temperature 
within  thirty  feet  of  the  surface,  yet  the  climate  could 
not,  on  that  account,  be  sensibly  different  from  what  it  is, 
or  the  soil  be  sensibly  more  or  less  genial  than  it  is  for  the 
roots  of  trees  or  smaller  plants."  § 

*  Whitney,  op.  tit.,  ?43-57.  t  Whitney,  op.  cit.,  121-204. 

J  W.  Thomson,  T'ranx.  Geol.  Soc.,  Glasgow,  v.  250. 

§  In  connection  with  this  we  are  reminded  of  the  summer  vegetation  of 
northern  Siberia  and  sub-arctic  America,  growing  luxuriantly  upon  a  soil  under- 
laid, at  the  depth  of  a  few  inches,  by  a  permanent  stratum  of  ice  or  frozen 
earth. 


GENERAL    REFRIGERATION.  487 

M.  Rey  de  Morande,  also,  has  recently  recorded  the  opin- 
ion tha£  "  the  great  uniformity  of  terrestrial  vegetation 
till  the  Cenomanian  epoch,  and  gradual  differentiation 
since,  according  to  latitude,  the  gradual  invasion  of  south- 
ern regions  by  trees  with  deciduous  leaves,  and  disappear- 
ance of  all  vegetation  in  polar  regions  are  phenomena " 
not  only  testifying  to  chang'es  in  terrestrial  climates,  but 
"explicable  only  by  gradual  diminution  of  solar  heat."* 

We  are  constrained,  therefore,  to  ascribe  the  lowering 
of  terrestrial  temperatures  to  the  secular  cooling  of  the 
sun.  No  other  theory  has  been  found  free  from  fatal 
objections.  Among  the  attempts  made  to  explain  the 
secular  cooling  of  climates,  "the  only  hypothesis  of  all 
hitherto  suggested  that  has  received  no  favor  from  any 
professed  geologist,  is  that  of  a  warmer  sun  —  the  one 
hypothesis  that  is  rendered  almost  infinitely  probable  by 
independent  physical  evidence  and  mathematical  calcula- 
tion.'^ 

We  seem,  therefore,  to  face  the  impressive  fact  that 
human  experience  is  able  to  testify  to  some  actual  abate- 
ment of  the  force  of  the  sun,  and  that  the  testimonies  of 
the  rocks  under  our  feet  affirm  and  extend  the  grand  con- 
clusion that  the  sun's  remoter  history  has  been  a  history  of 
cooling,  and  that,  consequently,  the  future  must  witness  a 
further  diminution  of  solar  light  and  heat. 

(2.)  Deductive  Considerations  Touching  Secular  Re- 
frigeration.— The  ultimate  refrigeration  of  the  sun  and 
planets  is  only  another  expression  for  the  dissipation  of  the 
energy  of  the  system.  As  all  the  forms  of  energy  in  the 
known  universe  are  mutually  convertible,  so,  also,  the 

*Nature,  xxvii,  119,  Nov.  30, 1882,  from  proceedings  of  Acad.  des  Sciences, 
Nov.  20,  1882. 

tSirW.  Thomson,  Trans.  Geol.  Soc.,  Glasgoiv,  v,  250.  Compare,  also,  id., 
iii,  16.  17.  Mr.  S.  V.  Wood  maintains  that  the  earth's  "glacial  period"  was 
caused  by  a  diminution  in  the  heat-emitting  powers  of  the  sun. — Geoloy.  Mag., 
July.  1882. 


488  PLANETARY    DECAY. 

tendency  of  the  universe  is  toward  the  transmutation  of 
all  other  forms  of  energy  into  heat.  The  tendency  of 
heat  is  toward  diffusion  and  equilibrium  through  the  pro- 
cesses of  radiation  and  conduction.  In  other  words,  the 
time  is  foreshadowed  when  all  parts  of  the  solar  system 
and  of  the  material  universe  will  have  attained  a  uniform 
thermal  condition,  and  all  exchanges  of  heat  will  have 
ceased.  And  this  is  the  finality  to  be  anticipated  after  all 
other  forms  of  energy  shall  have  been  transformed  into 
heat.  In  that  eventuality,  all  the  forces  of  nature  will 
have  attained  an  equilibrated  or  exhausted  condition.  No 
more  motion — no  more  light  or  electricity,  or  heat  —  the 
last  course  of  physical  change  will  have  been  complete. 

More  than  twenty-three  years  ago  I  was  led  to  the 
adoption  of  such  views,  and  recorded  them  in  these  words: 
"All  the  present  motions  of  the  universe,  whether  physical 
or  physiological,  are  but  the  phenomena  attendant  upon 
the  progression  of  matter  toward  a  state  of  ultimate  equi- 
librium. *  *  *  The  tendency  of  all  physical  forces 
toward  a  state  of  equilibrium  and  rest  will  result  in  a  com- 
plete equilibrated  diffusion  of  all  self-repellant  matter,  and 
a  concentration  into  one  mass  of  all  self-attractive  matter. 

*  *     *     It  is  not  likely  that  the  material  universe  is 
infinite.     *     *     *     When  light,  heat,  electricity  and  other 
'imponderable   agents'   (if  any)   shall   have   become   uni- 
formly distributed  throughout  matter,  and  have  thus  been 
brought  to  a  state  of  equilibrity,  both  in  themselves  and  in 
respect  to  matter,  there  can  not  be  either  sun,  star  or  other 
radiant  source  of  light  and  heat,  or  any  of  the  motions 
produced  by  these  agents  in  the  organic  and  inorganic 
worlds.     *     *     *     There  must  have  been  a  beginning  to 
this  series  of  evolutions."* 

*  The  Cycles  of  Matter,  or  the  Permanence  of  the  Earth  and  the  Destiny  of 
the  Race,  Michigan  Journal  of  Education,  viii,  273-8,   Aug.,   1860.     Compare 
Spencer's  chap,  xvi  (published  in  1862),  on  "  Equilibration,"  in  First  Principles. 


GENERAL    REFRIGERATION.  489 

Such  deductions,  however,  had  been  reached  by  Pro- 
fessor (now  Sir)  William  Thomson  eight  years  earlier, 
though  information  of  the  fact  had  not  reached  the  pres- 
ent writer.*  His  conclusions  are  as  follows:  (a)  "There  is 
at  present  in  the  material  world,  a  universal  tendency  to  the 
dissipation  of  mechanical  energy,  (b)  Any  restoration 
of  mechanical  energy  without  more  than  an  equivalent 
dissipation  is  impossible  in  inanimate  material  processes, 
and  is  probably  never  effected  by  means  of  organized 
matter,  either  endowed  with  vegetable  life  or  subjected  to 
the  will  of  an  animated  creature,  (c)  Within  a  finite 
period  of  time  past,  the  earth  must  have  been,  and  within 
a  finite  period  of  time  to  come,  the  earth  must  again  be, 
unfit  for  the  habitation  of  man  as  at  present  constituted, 
unless  operations  have  been,  or  are  to  be  performed,  which 
are  impossible  under  the  laws  to  which  the  known  opera- 
tions going  on  at  present  in  the  material  world  are  sub- 
ject,"t 

According  to  this  doctrine,  the  heat  of  our  system  — 
chiefly  solar  —  on  which  all  its  activities  depend,  is  under- 
going a  gradual  dissipation  in  infinite  space.  It  is  not 
annihilated,  but  it  is  lost  to  us.  In  the  distant  future,  all 
parts  of  the  system  will  be  reduced  to  the  mean  tempera- 
ture of  space,  and  the  wheels  of  the  organism  will  cease 
to  move. 

We  may  anticipate  that  the  cooling  sun  will  pass 
through  phases  similar  to  those  of  forming  planets.  A 
liquid  central  globe  will  grow,  and,  as  it  enlarges,  solidi- 

*  Professor  W.  Thomson's  Memoir,  On  a  Universal  Tendency  to  the  Dissi- 
pation of  Mechanical  Energy,  was  read  before  the  Royal  Society  of  Edinburgh, 
April  lit,  1852,  and  communicated  by  the  author  to  the  London,  Edinburgh  and 
Dublin  Philosophical  Magazine  for  publication,  October,  1852,  Series  IV,  vol.  iv, 
pp.  304-6. 

tSee  also  the  celebrated  essay  of  Helmholtz  on  the  Interaction  of  Xa'ural 
Forces,  first  presented  as  a  lecture  at  KOnigsberg,  in  1854  —  Correlation  and  Con- 
servation of  Forces,  Youman's  ed.,  242-4,  etc.  Mayer,  also,  glanced  in  the 
same  direction,  in  1851,  but  he  only  raised  a  query. —Id.  355. 


490  PLANETARY    DECAY. 

fication  will  appear  at  the  core.  It  will  become  incrusted. 
Its  light  will  grow  ruddy  and  dim.  The  vapors  of  water 
will  condense  in  the  sun's  atmosphere.  A  stormy  stage 
of  long  duration  will  ensue.  Surface  waters  will  accumu- 
late to  some  extent  upon  the  darkened  exterior.  We  may 
infer,  however,  that  the  relative  supply  of  water  will  be 
scant.  The  pores  of  the  fire-formed  rocks  will  eagerly 
drink  it  up.  The  cooled  and  planetary  surface  will 
emerge  from  the  tumult  of  the  secular  storm;  but  a  star- 
lit firmament  will  overhang  it.  Its  own  inherent  warmth 
may,  for  a  secular  period,  preserve  a  habitable  tempera- 
ture; but  if  organic  creatures  find  existence  on  it,  they 
must  possess  nocturnal  instincts.  Later  on  in  the  eterni- 
ties, this  sunless  planet — this  exhausted  and  planetized 
sun  —  will  have  felt  the  chill  of  surrounding  space.  In 
the  remotest  finality  which  deductive  science  can  reach, 
the  sun  and  planets  will  have  been  gathered  in  one  central 
mass.  All  fire  and  light  will  have  been  extinguished. 
No  relative  motion  will  survive  —  only  the  clead,  cold 
corse  will  rotate  on  an  axis  and  travel  onward  in  its  mys- 
terious, endless,  aimless  course  through  the  eternities  still 
to  come.* 

Thus,  by  the  telescope  of  deductive  science,  we  are 
able  to  glance  "through  the  corridors  of  time"  to  come, 
and  anticipate  with  assurance  the  approach  of  events  as 
remote  in  the  coming  direction  as  those  primordial  events 
in  the  opposite  direction  which  we  have  seen  connected 
with  the  cradle  of  the  Solar  System.  But  in  so  distant  a 
glance  all  perspective" is  lost.  Like  the  stars  in  the  firma- 
ment, those  events  are  projected  upon  one  common 
ground.  It  is  impossible  to  assert  in  what  order  these 
final  consummations  will  be  realized.  We  only  know  they 

*  The  present  writer  has  reflected  much  on  these  eventualities.  See,  besides 
the  memoir  already  cited,  The  Ladies'  Repository,  Cincinnati,  Nov.  and  Dec., 
1863,  and  Jan.,  1864;  Sketches  of  Creation,  1870,  380-431,  and  various  other 
publications. 


GENERAL    REFRIGERATION.  491 

are  inclosed  in  the  future.  The  sun  will  probably  assume 
a  planetary  condition  only  after  the  last  precipitations 
shall  have  taken  place.  The  continents  may  be  levelled 
before  the  synchronistic  stage  of  the  earth  and  moon  is 
reached.  The  precipitative  tendencies  of  tidal  action 
may  exceed  those  resulting  from  resistances  encountered 
in  planetary  space.  Whatever  the  order  of  progress  to- 
ward these  planetary  issues,  and  to  whatever  distance 
removed,  these  tendencies  are  so  many  categories  of 
change  which  demonstrate  that  a  terrestrial,  and  more 
generally  a  planetary,  and  even  a  cosmical,  finality  must 
be  reached.  The  world  is  finite  in  duration.  The  Solar 
System  is  finite.  The  entire  cosmical  organism  is  finite  in 
duration.  That  which  is  approaching  a  limit  to  its  exist- 
ence in  one  direction  has  proceeded  from  finite  limits  in 
the  opposite  direction.  There  was  a  time  when  the  cos- 
mical organism  beg-an  to  exist.  Even  if  it  was  an  older 
framework  reorganized,  it  was  a  new  beginning.  What- 
ever the  number  of  times  it  had  been  begun,  there  was  a 
first  time.  If  there  was  a  first  time,  then  at  that  moment 
cosmical  existence  was  out  of  the  order  of  causal  rela- 
tions in  the  natural  world.  If  there  was  not  a  first 
organization,  then  the  cosmic  organism  is  eternal;  it  does 
not  run  down  or  wear  out;  it  is  out  of  the  order  of 
causal  relations  in  the  natural  world. 

3.  Revivification  of  a  Dead  Universe. — The  ultimate 
precipitation  upon  the  sun  of  all  the  matter  in  our  system 
would  not  end  the  existence  of  matter  or  of  energy,  but 
only  the  existence  of  one  department  of  the  cosmic 
organism.  That  other  systems  have  already  attained  this 
condition  can  hardly  be  doubted.  Nor  is  it  easier  to 
doubt  that  in  the  exhaustless  and  perhaps  unexplored 
resources  of  the  cosmic  economy  some  means  exist  for 


492  PLANETARY    DECAY. 

restoration  of  an  effete  system  to  a  renewal  of  intense 
cosmical  activity.* 

Nor  would  the  complete  equilibrium  of  the  total  energy 
of  the  visible  universe  end  the  existence  of  matter  or  of 
energy.  We  must  still  believe  in  an  appointed  reexcita- 
tion  of  the  slumbering  potencies  of  the  cosmic  elements. 
By  what  natural  means  this  could  be  effected,  we  cannot 
even  surmise. 

A  suggestion  toward  a  possible  means  for  this  end  was 
made  by  Rankine  in  1852,  soon  after  the  appearance  of 
Thomson's  memoir. \  He  holds  that  the  interstellar  me- 
dium must  be  perfectly  transparent  and  diathermanous, 
and  thus  "incapable  of  acquiring  any  temperature  what- 
ever, and  all  heat  which  arrives  in  the  conductible  form  at 
the  limits  of  the  atmosphere  of  a  star  or  planet  will  there 
be  totally  converted,  partly  into  ordinary  motion  by  the 
expansion  of  the  atmosphere,  and  partly  into  the  radiant 
form.  The  ordinary  motion  will  again  be  converted  into 
radiant  heat,  so  that  radiant  heat  is  the  ultimate  form  to 
which  all  physical  energy  tends.  *  *  *  Let  it  now  be 
supposed  that  in  all  directions  round  the  visible  world  the 
interstellar  medium  has  bounds,  beyond  which  there  is 
empty  space.  Then,  on  reaching  those  bounds,  the  radi- 
ant heat  of  the  world  will  be  totally  reflected,  and  will 
ultimately  be  concentrated  into  foci.  At  each  of  these 
foci  the  intensity  of  heat  may  be  expected  to  be  such 
that  should  a  star  (being  at  this  period  an  extinct  mass  of 
inert  compounds)  in  the  course  of  its  motions  arrive  at 
that  part  of  space,  it  will  be  vaporized  and  resolved  into 

*  Spencer:  First  Principles,  Am,  ed.,  480.  So  Kant:  Kann  man  nicht  glau- 
ben,  die  Natur,  welche  vermOgend  war,  sich  aus  dein  Chaos  in  eine  regelmiissige 
Ordnung  und  in  ein  geschicktes  System  zn  setzen,  sei  ebenfalls  im  Standc  aus 
dem  nenen  Chaos,  darin  sie  die  Verminderung  ihrer  Bewegungen  versenkt  hat, 
sich  wiederum  eben  so  leicht  herzustellen,  und  die  erste  Verbindung  zu  erneu- 
ern?  — KANT,  Werke,  Hartenstein  ed.,  i,  302. 

t  W.  J.  M.  Rankine :  On  the  Reconcentration  of  the  Mechanical  Energy  of 
the  Universe,  Phil.  Mag.,  IV,  iv,  368-60,  Nov.,  1852. 


GENERAL    REFRIGERATION.  493 

elements.  *  *  *  These  opposite  processes  may  go  on 
together.  Some  of  the  luminous  objects  which  we  see  in 
distant  regions  of  space  may  be  not  stars,  but  foci  in  the 
interstellar  ether." 

The  improbability  of  this  curious  conception  impresses 
itself  at  once.  The  limitation  of  the  ethereal  vehicle  of 
starry  radiations  is  not  easy  to  grant,  though  thinkable. 
The  luminiferous  medium  is  not  perfectly  transparent  and 
diathermanous.  The  mode  of  action  by  which  the  radia- 
tions are  returned  is  too  mysterious  to  make  part  of  a 
hypothesis.  The  concentration  of  the  rays  is  equally  mys- 
terious. The  existence  of  moving  bodies  is  incompatible 
with  the  premise  of  a  full  equilibrium  of  cosmic  forces. 
And  finally,  if  all  these  doubts  could  be  removed,  the 
intense  focal  heat  contemplated  would  be  an  impossibility. 

The  last  point  has  been  fully  demonstrated  by  Clau- 
sius.*  He  proves  that  it  contravenes  the  second  law  of 
thermodynamics,  which  declares  that  "  it  is  impossible  by 
the  unaided  action  of  natural  processes,  to  transform  any 
part  of  the  heat  of  a  body  into  mechanical  work,  except 
by  allowing  heat  to  pass  from  that  body  into  one  of  a 
lower  temperature."  f  Clausius  has  simplified  the  expres- 
sion of  this  law  in  a  way  which  suits  the  present  case,  by 
stating  it  thus:  "  Heat  cannot  pass  of  itself,  i.  e.,  withoict 
compensation,  from  a  colder  to  a  warmer  body."  Now 
the  conception  of  Rankine  requires  that  radiations,  of 
energy  shall  be  concentrated  through  reflection,  in  such  a 
way  that  a  body  placed  at  a  focal  point  shall  become 
heated  to  a  higher  temperature  than  the  bodies  possess 
from  which  the  radiations  proceeded.  Clausius,  on  the 

*  R.  Clausius:  Ueber  die  Concentration  von  Warmeund  Lichtstrahlen  and 
die  Granzen  ihrer  Wirkung,  Pogg.  Annal.,  cxxi,  1-44, 1864,  read  at  the  Zurich 
Natural  History  Society,  June  22,  1863;  more  fully  elaborated  in  Die  Mechan- 
ischeWannetheorie,  2d  ed.,  i,  315-53. 

t  Maxwell:  Theory  of  Heat,  153 ;  Clausius:  Dig  Mechanitche  Wdrmetheorie . 
i,  72,  81,  82. 


494  PLAXETARY    DECAY. 

contrary,  proves  (1)  "  That  the  force  of  emission  of  a  body 
depends  not  alone  on  its  constitution,  but  also  on  the  na- 
ture of  the  surrounding  medium,  in  such  a  wav  that  the 
force  of  emission  in  different  media  is  inversely  as  the 
square  of  the  velocity  of  propagation  of  the  rays  in  the 
medium,  or  directly  as  the  square  of  the  coefficient  of 
refraction  of  the  medium,"  and  (2)  "That  the  second  law  of 
thermodynamics  is  valid  not  only  in  cases  where  no  con- 
centration takes  place,  but  equally  in  cases  where  it  takes 
place."  It  follows  that  no  such  method  of  reconcentration 
of  cosmical  energy  as  Rankine  sug'gested  is  compatible 
with  the  established  processes  of  nature.  Nor  is  science 
able,  at  present,  to  point  out  any  natural  means  by  which 
the  dissipation  of  energy  from  our  system  may  be  arrested, 
or  the  impending  equilibrium  of  energy  throughout  the 
universe,  again  disturbed. 

Nevertheless,  there  remains  to  us  an  abiding  convic- 
tion, as  expressed  by  Kant  in  the  middle  of  the  last  cen- 
tury, and  which  Mr.  Spencer  bases  on  a,  priori  grounds, 
that  the  activities  of  a  dead  universe  may  be  renewed. 
"  Motion,"  he  says,  "  as  well  as  matter,  being  fixed  in 
quantity,  it  would  seem  that  the  change  in  the  distribu- 
tion of  Matter  which  Motion  effects,  coming  to  a  limit  in 
whichever  direction  it  is  carried,  the  indestructible  Mo- 
tion thereupon  necessitates  a  reverse  distribution.  Ap- 
parently, the  universally  coexistent  forces  of  attraction 
and  repulsion,  which,  as  we  have  seen,  necessitate  rhythm 
in  all  minor  changes  throughout  the  Universe,  also  neces- 
sitate rhythm  in  the  totality  of  its  changes  —  produce  now 
an  immeasurable  period  during  which  the  attractive  forces 
predominating  cause  universal  concentration,  and  then  an 
immeasurable  period,  during  which  the  repulsive  forces 
predominating  cause  universal  diffusion  —  alternate  eras 
of  Evolution  and  Dissolution."  *  These  recurrences  of 

*  Spencer:  First  Principles,  483. 


GENERAL    REFRIGERATION.  495 

cosmical  activity  and  rest  were  traced  in  my  essay  of  1860, 
and  designated  "The  Cycles  of  Matter." 

The  reorganization  of  a  Universe  in  which  the  series 
of  events  has  reached  the  last  term  attainable  by  action 
according  to  known  laws,  presents  before  us  a  problem  of 
the  same  order  as  that  of  the  origination  of  matter  and 
energy.  It  may  not  be  necessary  to  despair  of  the  dis- 
covery of  the  natural  means  of  recuperation  of  worn-out 
systems;  but,  as  long  as  the  means  remain  undiscovered, 
it  is  philosophically  legitimate  to  contemplate  a  restitution 
by  the  intervention  of  such  power  as  was  exercised  in  the 
first  institution  of  cosmical  order,  and  in  the  origination  of 
the  matter,  the  efficiency  and  the  method  revealed  in  the 
living  cosmos. 


CHAPTER  V. 
HABITABILITY    OF  OTHER   WORLDS. 

Da  wir  durch  die  spectralanalyse  wissen,  dass  die  chemischen  Elemente, 
aus  den  Planeten  und  Fixsterne  bestehen,  nicht  toto  genere  von  den  auf  der 
Erde  anzutreffenden  verschieden  sind,  so  werden  wir  auch  beziiglich  der  organ- 
ischen  Entwickelungen  auf  den  Planeten  ilhnliche  Wirkung  schliessen  diirfen. 
— ZOLLNER. 

Toutes  les  verites  mathe'matiques  doivent  etre  les  memes  dans  1'dtoile  Sirius 
et  dans  notre  petite  loge. —  VOLTAIRE. 

L'homme  fait  pour  la  temperature  dont  il  jouit  sur  la  terre,  ne  pourrait  pas, 
s-elon  toute  apparence,  vivre  sur  les  autres  planetes;  mais  ne  doit-il  pas  y  avoir 
une  infinite"  d'organisations  relatives  aux  diverses  temperatures  des  globes  de 
cet  univers  ?— LAPLACE. 

If  the  reader  should  have  a  mind  to  amuse  himself  with  probable  guesses 
about  the  furniture  of  the  planets  of  our  solar  system,  what  countries  'tis  prob- 
able are  there,  what  vegetables  are  produced,  what  minerals  and  metals  are 
afforded,  what  animals  live  there,  what  parts,  faculties  and  endowments  they 
have,  with  much  more  to  the  same  purpose,  he  may  find  a  pleasant  entertain- 
ment in  the  great  Mr.  Christian  Huygens'  Cosmotheoros,  and  some  other  authors 
that  have  written  on  the  subject.— WILLIAM  DERHAM,  1714. 

§1.    SOME  REFERENCES  TO  LITERATURE  ON  THE 
SUBJECT. 

ri^HE  habitability  of  other  worlds  is  a  question  on  which 
-L  a  vast  amount  of  speculation  has  been  expended.  It 
has  been  the  general  belief  that  many  other  worlds  are 
inhabited.*  Dr.  Lardner  argued  the  habitability  of  the 

*  Giordano  Bruno:  De  VInflnlto  Universe  e  Mondi  lunumerabili,  1534: 
Christian  Huygens:  Cosmotheoros,  sive  de  Terris  Cales/ibus,  earumque  ornatu 
conjecture,  Huygenii  Opera,  torn,  ii,  645-722,  Eng.  translation,  Tfie  Celestial 
Worlds  Discovered,  or  Conjectures  concerning  the  Inhabitants,  Plants  and  Pro- 
ductions of  the  Worldsin  the  Planets,  1698,  2d  ed.  1722;  William  Derham:  Astro- 
theology,  1714,  3d  ed.  1717,  pp.  xlvii,  liii,  liv,  9th  ed.  1750,  pp.  xxx,  xxxiv,  xxxv : 
Immanuel  Kant:  Allgemeine  Naturgeschichte,  etc.,  1755,  3ter.  Theil,  s-iimnt- 
liche  Werke,i,  329-45;  Laplace:  Systeme  du  Monde,  5th  ed.,  1824,389;  Fonte- 
nelle:  Dialogues  on  the  Plurality  of  Worlds,  1686,  2d  ed.  1719;  Sir  David  Brew- 
ster:  More  Worlds  than  One;  C.  Flammarion:  LaPluraW.e  des  Mondes  Habites, 
496 


HUMAN   STANDARD    NOT   ABSOLUTE.  497 

moon  and  all  the  planets.*  Dr.  Brewster  held  similar 
views.  Some  have  even  maintained  that  the  physical  con- 
dition of  the  body  of  the  sun  may  be  such  as  to  produce  a 
state  of  habitability.  f  Sir  William  Herschel  is  said  to 
have  conjectured  that  the  solar  spots  are  the  highest  points 
—  some  600  miles  high  —  of  a  cool  and  habitable  globe.  J 
On  the  contrary,  the  habitability  of  other  worlds  has 
been  denied  on  theological  grounds.  §  It  was  formerly  a 
common  theological  belief  that  the  biblical  teaching  is  in- 
compatible with  the  doctrine  of  other  worlds  of  beings. 
Dr.  Whewell  disputed  the  plurality  of  worlds  by  appeal  to 
scientific  evidence.  || 

§2.   THE  HUMAN  STANDARD  OP  HABITABILITY  NOT 
ABSOLUTE. 

The  question  of  the  habitability  of  other  worlds  has 
generally  been  discussed  from  the  assumption  that  all  other 
corporeal  beings  must  be  clothed  in  flesh  and  bones  sim- 
ilar to  those  of  terrestrial  animals,  and  must  be  adapted  to 
a  similar  physical  environment.  But  it  is  manifest,  on  a 
moment's  consideration,  that  corporeality  may  exist  under 
very  divergent  conditions.  It  is  not  at  all  improbable  that 
substances  of  a  refractory  nature  might  be  so  mixed  with 
other  substances,  known  or  unknown  to  us,  as  to  be  capable 

8vo.,  1864;  R.  A.  Proctor:  Other  Worlds  than  Ours  ;  C.  Du  Prel:  Die  Planeten- 
bewohner  und  die  Nebularhypothese,  Neue  Studien  zur  Entwickelungsgeschichte 
des  Weltalls,  gr.  8°,  Leipzig,  1880;  Bentley:  Boyle  Lectures,  Lect.  viii,  ed.  1724, 
p.  298,  seq. ;  W.  Miller:  The  Heavenly  Bodies,  their  Nature  and  HabilabUily,  344 
pp.,  London,  1883. 

*  Lardner :  Museum  of  Science  and  Art. 

t  President  Forbes :  Reflections  on  the  Sources  of  Incredulity  ivith  regard  to 
Religion,  Edinb.  1750,  p.  3;  Dr.  Elliot,  Edinb.  Encyc.,  Art.  Astronomy,  vol.  ii, 
616;  Gentlemen's  Magazine,  1767,  63(5.  Compare  also  the  works  of  Flammarion, 
Jean  Reynaud,  Babinet  and  Pioger. 

ii  have  not  yet  found  this  opinion  recorded  in  his  writings. 

§  Maxwell:  Plurality  of  Worlds,  1820.  He  holds  that  the  Newtonian  phil- 
osophy contains  principles  "  which  lie  at  the  foundation  of  all  atheistical  sys- 
tems/' 

]  Whewell:  Of  the  Plurality  of  Worlds. 
32 


498  HABITABILITY   OF   OTHER   WORLDS. 

of  enduring  vastly  greater  vicissitudes  of  heat  and  cold 
than  is  possible  with  terrestrial  organisms.*  The  tissues  of 
terrestrial  animals  are  simply  suited  to  terrestrial  condi- 
tions. Yet  even  here  we  find  different  types  and  species 
of  animals  adapted  to  the  trials  of  extremely  dissimilar 
situations. 

Nor  is  it  to  be  supposed  that  the  plans  of  structure  of 
animals  on  other  habitable  planets  bear  necessarily  any 
analogy  to  organic  plans  on  the  earth.  That  an  animal 
should  be  a  quadruped  or  a  biped  is  something  not  depend- 
ing on  the  necessities  of  organization,  or  instinct,  or  in- 
telligence. That  an  animal  should  possess  just  five  senses 
is  not  a  necessity  of  percipient  existence.  There  may  be 
animals  on  the  earth  which  neither  smell  nor  taste.  There 
may  be  beings  on  other  worlds,  and  even  on  this,  who  pos- 
sess more  numerous  senses  than  we.  The  possibility  of 
this  is  apparent  when  we  consider  the  high  probability  that 
other  properties  and  other  modes  of  existence  lie  among 
the  resources  of  the  cosmos,  and  even  of  terrestrial  matter. 

There  are  animals  which  subsist  where  rational  man 
would  perish  —  in  the  soil,  in  the  river  and  the  sea.  No 
reason  can  be  assigned  why  aquatic  respiration  should  be 
confined  to  brute  animals.  On  a  planet  without  land,  like 
Uranus,  high  intelligence  might  be  enframed  in  a  gill- 
bearing  embodiment;  and  resources  and  stimuli  for  intel- 
lectual activity  might  be  discovered  in  the  bottom  of  the 
ocean,  or  in  the  infinitesimal  world  which  fills  a  slimy  pool, 
or  "swarms  upon  the  thickly  peopled  air.''  Nor  is  incor- 
porated rational  existence  conditioned  on  warm  blood,  nor 
on  any  temperature  which  does  not  change  the  forms  of 
matter  of  which  the  organism  may  be  composed.  There 
may  be  intelligences  corporealized  after  some  concept  not 

*  While  these  pages  are  in  the  printer's  hands,  similar  suggestions  appear 
from  others.  See  Charles  Morris,  Amcr.  Naturalist,  xvii,  9.30-1,  Sept.,  1883,  and 
B.  D.  Cope,  Science,  ii,  279,  Aug.  31, 1883,  in  an  address  at  Minneapolis. 


HUMAN   STANDARD   NOT   ABSOLUTE.  499 

involving  the  processes  of  injestion,  assimilation  and  re- 
production. Such  bodies  would  not  require  daily  food  and 
warmth.  They  might  be  lost  in  the  abysses  of  the  ocean, 
or  laid  up  on  a  stormy  cliff  through  the  tempests  of  an 
arctic  winter,  or  plunged  in  a  volcano  for  a  hundred  years, 
and  yet  retain  consciousness  and  thought.  It  is  conceiv- 
able. Why  might  not  psychic  natures  be  enshrined  in  in- 
destructible flint  and  platinum?  These  substances  are  no 
further  from  the  nature  of  intelligence  than  carbon,  hydro- 
gen,, oxygen  and  lime.  But,  not  to  carry  the  thought  to 
such  an  extreme,  might  not  high  intelligence  be  embodied 
in  frames  as  indifferent  to  external  conditions  as  the  sage 
of  the  western  plains  or  the  lichens  of  Labrador — the 
rotifers  which  remain  dried  for  years  or  the  bacteria  which 
pass  living  through  boiling  water.  Again,  there  is  no 
reason  why  a  given  amount  of  light  should  accompany 
intelligent  organization.  Many  animals,  not  among  the 
least  intelligent,  find  the  night  their  appropriate  period  of 
activity.  Some  exist  and  thrive  in  rayless  caverns  and 
ocean  depths.  On  a  planet  dimly  lighted,  like  Neptune, 
men  might  be  organized  with  pupils  as  large  as  silver  dol- 
lars, or  even  as  large  as  dinner  plates.  Vision  might  be  as 
distinct  on  Neptune  as  on  the  earth.  As  to  warmth,  a 
blanket  of  vapors  may  keep  it  in  and  accumulate  it  to  the 
requisite  extent.  And  in  that  distant  time  when  the  sun 
shall  become  planetary,  large-orbed  men  may  move  about 
in  star  light  over  a  surface  sufficiently  warmed  by  internal 
heat,  and  forms  of  vegetation  may  flourish,  and  supply 
food  for  man  and  beast  without  the  stimulus  of  solar  radia- 
tions. These  suggestions  are  made  simply  to  remind  the 
reader  how  little  can  be  argued  respecting  the  necessary 
conditions  of  intelligent,  organized  existence,  from  the 
standard  of  corporeal  existence  found  upon  the  earth. 
Intelligence  is,  from  its  nature,  as  universal  and  as  uniform 
as  the  laws  of  the  universe.  Bodies  are  merely  the  local 


500  HABITABILITY   OF   OTHER   WORLDS. 

fitting  of  intelligence  to  particular  modifications  of  univer- 
sal matter  and  force. 

§3.    HABITABILITY  UNDER  THE  HUMAN  STANDARD. 

But  let  us  consider  how  far  other  worlds  are  suited  for 
habitations  for  beings  akin  to  ourselves.  This  is  a  question 
for  scientific  consideration.  The  answer  to  the  question, 
when  asked  with  reference  to  each  of  our  planets,  is  to 
be  sought  in  what  has  been  already  said  concerning  the 
physical  conditions  of  the  planets.  Mercury  is  not  habit- 
able for  beings  like  ourselves.  Proximity  to  the  sun 
results  in  a  destructive  degree  of  heat,  if  it  does  not 
actually  prevent  all  water  from  finding  a  resting  place  on 
the  planet's  surface.  The  sun's  apparent  diameter  from 
Mercury  is  more  than  two  and  a  half  times  as  great  as 
from  the  earth. 

In  reference  to  Venus,  and  possibly  also  Mercury,  we 
must  bear  in  mind  that  the  relations  of  heat  and  water 
are  such  that  water  might  exist  as  a  dense  and  permanent 
envelope  of  clouds.  This  seems  the  more  probable,  even 
for  Mercury,  in  view  of  Professor  Langley's  determination 
of  the  astonishing  rate  of  radiation  in  a  thin  atmosphere. 
At  the  upper  limit  of  an  atmosphere  sufficiently  dense  to 
support  aqueous  vapor,  it  seems  not  irrational  to  assume 
that  escape  of  heat  would  be  rapid  enough  to  condense 
water  even  in  the  fierce  solar  heat  experienced  at  Mercury's 
distance  from  the  sun.  So  far  as  the  existence  of  a 
stratum  of  clouds  is  possible,  this  would,  of  course,  serve 
as  a  screen  for  the  surface  of  the  planet,  so  that  compara- 
tively little  of  the  sun's  direct  radiation  would  interfere 
with  habitability.  In  this  view  there  seems  no  great  im- 
probability that  both  these  planets  are  inhabited  by  intel- 
ligences organized  somewhat  like  ourselves.  The  amount 
of  water  belonging  to  these  planets  being  in  less  propor- 
tion than  on  the  earth,  the  processes  of  evaporation  and 


HABITABILITY    UNDER   THE    HUMAN   STANDARD.    501 

precipitation  must  keep  it  in  active  circulation.  No  very 
considerable  bodies  of  water  can  be  supposed  to  exist, 
and  a  large  proportion  of  the  entire  surface  must  be  ac- 
cessible to  occupation  and  cultivation.  The  final  absorp- 
tion of  the  water  will,  therefore,  occur  at  a  relatively 
early  epoch,  when,  of  course,  habitability  must  end. 

Thus,  the  first  thought  of  these  sister  worlds  suggests 
that  they  may  be  the  homes  of  beings  kindred  to  our- 
selves. Then  the  knowledge  of  the  intensity  of  the  solar 
radiations  on  their  surfaces  seems  to  preclude  the  belief  in 
their  habitability.  But  finally,  a  discovery  of  natural 
means  for  the  alleviation  of  excessive  heat  leaves  us  with 
the  conviction  that  after  all  we  may  have  neighbors  on 
the  contiguous  planetary  territory.  As  to  their  organiza- 
tion, while  it  is  profoundly  true  that  under  circumstances 
extremely  diverse  from  those  under  which  we  live,  ex- 
tremely diverse  organizations  must  be  conceived  both 
possible  and  probable;  yet  where  the  divergence  is  no 
greater  than  on  the  interior  planets,  all  the  fundamental 
functions  and  processes  may  be  conceived  analogous  to 
our  own.  There  is  so  widespread  uniformity  in  the  nature 
and  action  of  physical  forces  that  we  may  suspect  the 
same  in  regard  to  organic  structures  and  activities.  As 
organization  in  its  forms  and  functions  is  conditioned  by 
the  properties  of  matter  and  the  laws  of  energy,  and 
these  conditions  are  widely  pervasive  throughout  our  sys- 
tem, we  have  good  ground  for  believing  that  plans  of 
organization  and  modes  of  activity  are  fundamentally 
analogous  under  all  planetary  conditions  not  more  diverse 
than  we  conceive  those  of  the  earth  and  the  interior  plan- 
ets to  be.  In  fact,  there  exist  contrasts  of  condition  upon 
the  earth  nearly  as  wide  as  the  contrasts  between  the 
earth  and  Venus.  In  all  these  contrasted  situations 
nature  employs  the  same  fundamental  plans  of  organ- 
ization and  functioning. 


502  HABITABILITY    OF    OTHER    WORLDS. 

On  the  whole,  as  intelligence  must  be  revealed  in  the 
cosmic  organization  of  Mercury  and  Venus,  there  are  pre- 
sumably intelligent  beings  in  correlation  with  the  intelligi- 
ble world;  and  as  the  conditions  of  corporeality  are  so  far 
analogous  to  those  on  the  earth,  we  may  reasonably  con- 
ceive organic  intelligences  on  those  planets  who  have 
power  of  locomotion  by  muscles  and  bones;  who  eat  and 
respire;  who  suffer  and  enjoy;  who  cognize  light  and  heat 
and  sound;  who  observe  and  reflect,  imagine  and  aspire; 
and,  while  ignorant,  probably,  of  many  or  most  of  our 
arts,  have  invented  many  others  of  which  we  never 
dreamed,  and  achieve  accomplishments  which  would  be 
miracles  to  us. 

The  moon,  in  the  absence  of  air  and  water,  must  be 
without  inhabitants  akin  to  ourselves.  Though  the  moon 
has  passed  through  the  successive  phases  of  a  cooling 
globe,  I  cannot  think  the  violence  which  must  have 
reigned  on  its  surface  before  synchronistic  times  would 
have  permitted  the  existence  of  an  organic  being.  Nor, 
since  the  synchronistic  period  began,  have  the  conditions, 
as  far  as  we  can  judge,  been  endurable.  The  fortnightly 
alternations  of  extreme  heat  and  extreme  cold  must  prove 
fatal  to  all  organic  life  with  which  we  are  acquainted.  It 
is  pleasant  to  think  of  kindred  beings  on  a  neighboring 
world,  though  we  might  not  by  any  possibility  open  inter- 
course with  them.  It  is  pleasant  even  to  believe  that  the 
moon  may  have  been  inhabited  in  a  former  planetary 
period.  It  creates  a  sense  of  relation  to  distant  parts  of 
the  universe  to  believe  that  other  beings  may  even  have 
lived  there  and  passed  away.  To  know  that  the  lunar 
surface  is  a  wild  scene  of  desolation,  and  to  know  that 
only  the  unconscious  forces  of  inorganic  nature  have  ever 
interrupted  the  oppressive  silence  of  the  planetary  soli- 
tude, seems  to  sunder  a  bond  of  sympathy  with  the  uni- 
verse, and  isolate  mankind  on  an  island  rock  where  no 


HABITABILITY    UNDER   THE   HUMAN    STANDARD.    503 

message  can  ever  arrive.  But  it  is  better  to  know  the 
truth  than  to  indulge  in  fancy.  The  moon  is  probably  no 
more  uninhabitable  in  the  present  period  than  it  has  been 
during  its  entire  history.* 

Mars,  according  to  the  scientific  indications,  presents 
conditions  more  nearly  approximating  the  demands  of 
habitability  than  any  other  planet  besides  the  earth.  It 
seems  almost  certain,  however,  that  the  meridian  of  its  hab- 
itable phase  is  passed.  The  sun's  apparent  diameter  from 
Mars  is  two-thirds  his  size  seen  from  the  earth,  and  his 
light  and  heat  are  only  three-eighths  as  much  as  the  earth 
receives.  As  the  intensity  of  gravity  on  the  surface  of 
Mars  is  only  three-eighths  the  intensity  of  gravity  on  the 
earth,  many  diverse  conditions  would  be  introduced.  A 
man  of  ordinary  agility  would  be  able  to  leap  over  a  wall 
twelve  feet  high.  If  on  the  earth,  a  strong  man  is  able  to 
support  26  pounds  in  his  palrn  at  arm's  length,  and  his 
arm  is  equivalent  to  four  pounds  in  his  palm,  he  might  be 
42^  feet  high  before  the  weight  of  his  arm  would  become  too 
great  for  him  to  extend  it;  but  on  the  planet  Mars,  such 
a  man  might  be  109  feet  in  height,  f  Again,  considering 

*  In  my  brochure,  entitled  Geology  of  the  Stars,  speaking  of  the  compara- 
tively rapid  succession  of  lunar  periods,  I  said:  "The  zoic  age  of  the  moon 
was  reached  while  yet  our  world  remained,  perhaps,  in  a  glowing  condition.  Its 
human  period  was  passing  while  the  Eozoon  was  solitary  occupant  of  our 
primeval  ocean."  Mr.  Fisk,  in  his  Cosmic  Philosophy  (i,  400,  note),  has  cited 
this  as  '•  an  example  of  the  too  hasty  kind  of  inference  which  is  often  drawn  in 
discussing  the  question  of  life  upon  other  planets."  Mr.  Fisk  misapprehends, 
for  it  is  not  stated  that  human  beings  ever  lived,  or  could  have  lived,  upon  the 
moon.  The  allusion  is  simply  to  that  stage  of  lunar  evolution  which  corre- 
sponded to  the  human  stage  in  terrestrial  evolution. 

t  If  w  =  the  total  weight  a  strong  man's  arm  can  support,  including  weight 
of  arm  and  load,  and  p  =  weight  of  arm,  and  n  equal  number  of  times  greater, 
in  any  dimension,  the  arm  is  which  could  bear  no  load,  then  n  =  ™  (Young's 
Mechanics,  Williams'  ed.,  p.  113),  and  if  g'  =  gravity  on  any  planet  compared 
with  gravity  on  the  earth,  then,  on  that  planet 


Now,  if  we  assume  that  a  man  can  raise  26  pounds  at  arm's  length,  and  that 
his  arm  is  equal  to  4  pounds  in  his  palm,  then  n  =  7.5;  and  if  a  strong  man's 


504  HABITABILITY    OF   OTHER    WORLDS. 

that  the  Martial  atmosphere  is  likely  to  be  .105  that  of  the 
earth,  and  is  spread  over  .2828  the  same  amount  of  sur- 
face its  density  on  the  surface  of  the  planet  is  only  .1379 
that  of  the  earth's  surface  atmosphere,  giving  a  pressure 
on  the  mercurial  barometer  of  about  4.14  inches.  The 
height  of  the  Martial  atmosphere  reduced  to  uniform  sur- 
face density  would  be  2.694  times  that  of  the  earth's 
atmosphere,  or  about  13.56  miles.  The  surface  density  of 
the  Martial  atmosphere  is  only  such  as  would  be  attained 
on  the  earth  at  the  height  of  10.2  miles.*  This  implies  a 
universal  state  of  atmospheric  tenuity  on  the  surface  of 
Mars  which  has  not  been  found  compatible  with  any  ter- 
restrial life.  The  simple  difference  in  mass  creates  condi- 
tions which  would  render  the  surface  of  Mars  completely 
untenable  by  any  human  being;  and  this  consideration,  it 
might  have  been  stated,  applies  as  well  to  Mercury  and 
the  Moon.  But  this  is  no  proof  that  organic  beings 
suited  to  such  atmospheric  pressure  do  not  exist.  Ani- 
mals are  dredged  from  oceanic  depths  where  the  pressure 
as  much  exceeds  the  sea  level  pressure  as  the  atmospheric 
density  of  Mars  falls  below  the  terrestrial  standard.  Ani- 
mals are  adapted  as  they  are  because  the  conditions  are 
as  they  are;  and  we  may  feel  assured  that  if  the  condi- 
tions were  different,  organic  adaptations  would  be  differ- 
ent correspondingly.  The  conceivable  range  of  adapta- 

height  is  68  inches,  the  height  of  a  man  on  the  earth  who  could  barely  extend 
his  arm  — since  his  height  is  proportional  to  his  arm's  length  — would  be  68 
inches  X  7.5  =  42.5  feet ;  and  the  height  of  such  a  man  on  Mars  would  be 

^5.  =  108.95  feet. 


at  sea  level,  then,  since  the  density  diminishes  in  a  geometrical  ratio  as  the 
height  increases  in  an  arithmetical  ratio,  the  height  2  A  will  give  a  density  of 

~;  the  height  3  A  will  give  a  density  of  —'and  generally  the  height  x  h  will 
give  a  density  of  -^-  But  jL-=  .1379,  whence,  if  n  -  2  and  h  =  2.705  miles,  x 
=  3.77  and  x  h  =  3.77  X  2.705  =  10.2  miles. 


HABITABILITY    UNDER   THE    HUMAN   STANDARD.    505 

tions  is  limited  only  by  the  physical  properties  of  inorganic 
matter. 

On  the  planet  Jupiter,  the  mass  so  much  exceeds  that 
of  the  earth  that  all  the  relative  conditions  are  reversed. 
I  have  shown  that  atmospheric  density  is  nearly  6£  times 
as  great  as  on  the  earth.  Hence  respiration  would  only 
need  to  be  6^  times  less  active.  On  the  contrary,  the  force 
required  to  sustain  the  body  against  gravity  would  be  more 
than  2-i-  times  as  great,  and  all  weights  would  be  2|  times 
as  difficult  to  move.  This  increased  weight  of  the  body 
and  limbs  would  render  comparatively  less  efficient  similar 
muscular  efforts,  while  the  gravitational  resistances  to  be 
overcome  would  be  greater.  A  man  16^  feet  high  would 
be  barely  able  to  extend  his  arm  at  a  right  angle  with  his 
body.  If  ever  the  planet  Jupiter  attains  a  habitable  con- 
dition its  organic  beings  will  be  limited  in  some  such  man- 
ner as  these  numerical  results  imply. 

The  apparent  diameter  of  the  sun  from  Jupiter  is  only 
.2392  or  ^  the  same  from  the  earth;  and  the  sun's  radiant 
energies  in  the  forms  of  light,  heat,  actinism  and  attrac- 
tion, are  only  fa  of  the  same  at  the  earth.  Were  the 
sun's  heat  reduced  on  the  earth  to  -fa  its  present  amount, 
it  is  manifest  that  all  organic  life  must  perish.  If  ever, 
therefore,  the  inherent  temperature  of  Jupiter  subsides  so 
far  as  to  bring  his  surface  condition  to  that  of  the  earth, 
no  Jovian  climate  will  be  such  as  animal  organization  can 
endure.  As  his  actual  surface  temperature,  however,  will 
always  be  compounded  of  the  effects  of  solar  radiation 
and  of  conduction  from  within,  there  will  be  an  epoch 
when  his  actual  mean  surface  temperature  will  be  the 
same  as  the  earth's  actual  mean  surface  temperature.  The 
vicissitudes  of  the  seasons  will  be  -fa  as  g'reat  as  on  the 
earth  —  regardless  of  the  effect  of  less  obliquity  of  the 
axis — and  the  diurnal  and  nocturnal  fluctuations  of  tem- 
perature will  be  only  -fa  as  great.  Owing  to  a  denser  at- 


506  HABITABILITY    OF   OTHER    WORLDS. 

mosphere,  the  fluctuations  will  be  even  less  than  this. 
The  higher  inherent  temperature  of  the  soil  will  result  in 
so  much  radiation  from  the  planet  that  on  a  planet  with 
so  large  a  supply  of  water,  and  in  an  atmosphere  so  dense 
as  Jupiter's  the  sun's  deficient  heat  may  be  largely  com- 
pensated by  suppressed  radiation  from  the  planet.  The 
situation  will  be  that  of  a  mild  and  dimly  lighted  "stove" 
in  horticultural  operations,  highly  suitable  for  the  growth 
of  mushrooms.  Itjvvill  be  perpetual  evening.  It  can  not 
be  doubted  that  corporeal  intelligences  might  be  coordi- 
nated to  such  a  physical  condition.  For  the  present,  how- 
ever, we  have  not  the  slightest  grounds  for  imagining  the 
existence  of  organic  populations  upon  the  surface  of 
Jupiter,  unless  they  depart  in  some  very  extreme  way 
from  the  terrestrial  standard. 

As  to  the  planets  remoter  from  the  sun,  I  have  offered 
reasons  for  considering  them  advanced  to  a  state  of  total 
refrigeration.  They  cannot  therefore,  be  conceived  as 
habitable.  There  was  a  time,  however,  in  the  history  of 
each,  when  its  stage  of  cooling  produced  a  surface  tem- 
perature suited  for  organic  life.  At  that  stage,  the  re- 
lations of  organic  beings  on  their  surfaces  were  similar  to 
those  which  may  be  anticipated  for  Jupiter,  with  all  the 
greater  divergences  from  the  terrestrial  condition  which 
depend  on  distance  from  the  sun  carried  to  successively 
greater  extremes,  and  successively  larger  proportions  of 
water  and  gaseous  substances.  On  Neptune  the  apparent 
diameter  of  the  sun  is  but  -fa  the  sun's  apparent  diame- 
ter to  us,  and  his  heat  and  light  are  reduced  to  -$fo  the 
heat  and  light  received  by  the  earth.  This  light  would, 
nevertheless,  be  equal  to  about  69  of  our  moons.  The 
excess  of  water  however,  on  all  the  distant  planets,  in  ac- 
cordance with  views  heretofore  presented,  would  probably 
render  them,  in  all  stages  of  existence,  totally  uninhabit- 
able for  beings  like  ourselves.  But  it  is  always  to  be  re- 


HABITABIL1TY    UNDER   THE   HUMAN    STANDARD.    507 

raembered  that  other  beings  suited  to  the  actual  exigences 
of  the  environment,  may  have  occupied  the  situation. 

The  earth,  then,  so  far  as  we  can  reason,  is  in  the  middle 
of  the  habitable  zone  of  the  solar  system,  if  our  own  na- 
tures are  assumed  as  the  criterion  of  habitability.  On 
either  side,  the  rigor  of  the  physical  conditions  seems  to 
proclaim  our  system  a  voiceless  and  lifeless  desert.  Even 
our  near  neighbor,  the  moon,  lies  on  the  borders  of 
this  desert.  Within  the  vast  limits  of  the  solar  system 
there  is  but  one  happy  niche  where  corporeal  organization 
according  to  our  standard  can  enter  into  material  relations 
with  the  physical  environment.  The  conclusion  is  un- 
doubtedly disappointing.  But  the  impression  is  further 
deepened  by  the  reflection  that  on  our  own  congenial 
planet  life  is  hemmed  in  between  the  terrestrial  surface 
and  the  upper  limit  of  a  film  of  atmosphere  not  thicker 
than  the  mean  depth  of  the  film  of  ocean  which  enwraps 
the  solid  globe.  The  entire  human  family  swarms  within 
a  sheet  of  atmosphere  not  over  three  miles  thick.  Above, 
are  the  rigors  of  unendurable  cold,  and  the  horrors  of  un- 
supported respiration.  Below,  are  the  impenetrable  rocks 
or  the  submerging  waves  or  the  internal  fires.  Even-  the 
space  about  us  and  nearest  to  us  is,  for  the  greater  part, 
inaccessible  to  man,  and  unvisited  by  any  organic  being. 
We  need  not  wonder  that  corporeal  existence  is  a  rarity 
through  all  the  realm  of  our  system. 

But  there  are  other  suns  and  other  planetary  systems, 
and  other  worlds  which  possess  the  conditions  of  habita- 
bility. When  we  look  on  the  hosts  of  stars,  and  consider 
that  if  only  one  habitable  planet  wanders  about  each  sun, 
we  understand  that  the  number  of  habitable  worlds  is 
countless.  In  this  view,  space  seems  to  be  densely  popu- 
lated. We  have  neighbors  ;  they  live  beyond  impas- 
sable barriers,  but  they  gaze  on  the  same  galaxy,  and 
we  know  they  are  endowed  with  certain  faculties  which 


508  HABITABILITY   OF   OTHEE    WORLDS. 

establish  a  community  between  them  and  us.  How- 
ever conformed  bodily,  whatever  their  modes  and  means 
of  organic  activity,  we  know  that  they  reason  as  we 
reason,  and  interpret  the  universe  on  the  same  princi- 
ples of  logic  and  mathematics  as  ourselves.  The  or- 
bits which  their  planetary  homes  describe  are  ellipses  ; 
they  have  studied  the  same  celestial  geometry  as  our- 
selves ;  they  have  written  their  treatises  on  celestial 
mechanics  ;  they  have  felt  the  impact  of  the  luminous 
wave  of  ether ;  they  have  speculated  on  the  nature  of 
matter  and  energy ;  they  have  interpreted  the  order  of 
the  cosmical  mechanism  as  the  expression  of  thought  and 
purpose  ;  they  have  placed  themselves  in  communion  with 
the  Supreme  Thinker,  who  is  so  near  to  all  of  us  that 
his  voice  is  audible  alike  to  the  ear  of  reason  in  all  the 
worlds. 


PART  III. 
GENERAL  COSMOGONY. 


Das  All  einem  jener  eudlichen  Baume  gleicht  an  clenen  zu  denselben  Zeit, 
hier  eine  Bliithe  aufgeht,  dort  einc  Frucht  von  Zweige  fiillt. — STRAUSS. 

Auf  gleiche  Weise  verlassen  ganze  Welten  und  Systeme  den  Schauplatz, 
nachdem  sie  ihre  Rolle  ausgespielt  haben.  *  *  *  Indessen,  dags  die  Natur 
mit  veranderlichen  Auftritten  die  Ewigkeit  ausziert,  bleibt  Gott  in  einer  unauf- 
horlichen  Schopfung  geschaftig,  den  Zeug  zur  Bildung  noch  grosserer  Welten 
zu  formen.— KANT. 

Mit  welcher  Art  der  Ehrfurcht  muss  nicht  die  Seele  sogar  ihr  eigen  Wesen 
ansehen,  wenn  sie  betrachtet,  dass  sie  noch  alle  diese  Veranderungen  iiberleben 

SOll.-KANT. 


CHAPTEE  I. 

FIXED    STARS    AND    NEBULAE. 
§  1.   CONDITIONS  OF  THE  FIXED  STARS. 

1.   Double,  Triple  and  Multiple  Stars. 

THAT  some  of  the  fixed  stars  are  the  result  of  the 
gradual  condensation  of  nebulous  matter  about  a 
centre  was  the  conjecture  of  Sir  William  Herschel.  I  be- 
lieve that  the  stars  in  general  have  resulted  from  nebular 
condensation;  but  in  many  cases  —  probably  not  in  all  — 
a  rotation  has  arisen  whose  influence  has  been  perma- 
manently  impressed  on  the  course  of  events.  The  con- 
dition of  our  own  system,  and  the  history  deduced  from 
it,  make  known  a  natural  and  probable  mode  of  evolution 
of  other  systems;  and  it  cannot  reasonably  be  denied 
that  many  other  systems  have  come  into  existence  in 
a  similar  way.  Other  planets,  consequently,  revolve  in 
nearly  circular  orbits  about  many  other  suns.  It  is  not 
impossible,  however,  that  a  non-rotating  sun  should  be 
attended  by  planets  which  have  not  been  disengaged  from 
its  own  mass.  It  is,  indeed,  probable,  that  many  small 
cosmical  bodies  should  have  been  thrown  by  contending 
attractions  into  paths  which  pass  near  great  centres  of 
attraction.  While  many  of  these  must  have  moved  with 
velocities  which  would  carry  them  on  in  hyperbolic  curves, 
others  may  have  moved  with  velocities  so  low  as  to  pass 
into  elliptic  orbits,  and  thus  become  planets  or  satellites 
to  greater  bodies.  The  comets  of  our  own  system  seem 
to  realize  both  these  conjectures.  But  a  planetary  rela- 
tion established  in  this  manner  would  present  an  orbit  of 

511 


512  FIXED   STABS   AND    NEBULAE. 

high  eccentricity.  Moreover,  it  seems  probable,  consider- 
ing the  immensity  of  the  intervals  of  space,  and  the  great 
distance  from  which  a  smaller  mass  would  approach  a 
greater,  that  in  nearly  all  cases  a  velocity  would  be  ac- 
quired too  great  for  the  assumption  of  elliptic  orbits.  This 
would  be  especially  the  case  with  approaching  bodies 
having  sufficient  mass  to  constitute  a  planet.  More  insig- 
nificant collections  of  matter  would  be  more  under  the  con- 
trol of  central  masses.  Hence  foreign  bodies  introduced 
into  a  system  would  be  more  probably  of  a  cometary  than 
of  a  planetary  character. 

That  other  suns  are  attended  by  planets  is  a  fact  of 
observation;  though  no  planetary  attendant  would  be  visi- 
ble except  such  as  retain  still  an  incandescent  character. 
Hundreds  and  even  thousands  of  stars  have  been  pro- 
nounced "double;"  and,  in  a  number  of  cases,  the  two 
components  have  been  observed  in  a  process  of  revolution 
about  the  common  centre  of  gravity.*  Not  less  than 
fifteen  of  these  have  been  observed  sufficiently  long  to 
determine  their  periods  of  revolution;  and  several  have 
been  actually  traced  through  complete  revolutions,  f 

It  needs  hardly  be  said  that  no  attendant  of  a  sun 
would  be  visible  unless  itself  of  very  great  magnitude,  and 
hence  having  sufficient  mass  to  compel  a  visible  amount 
of  motion  in  its  nominal  central  body.  How  many  smaller, 
and  therefore,  invisible,  planets  though  still  luminous, 
and  how  many  smaller  and  darkened  planets,  may  revolve 
about  the  same  centre,  is  matter  open  to  conjecture;  but 

*Struve,  in  Mensurce  Mcrometricce,  Dorpat,  1837,  enumerated  3,000  double 
stars,  most  of  which  had  been  noted  by  Sir  William  Herschel.  To  this  number 
Otto  Struve"  of  Pulkova  has  added  500;  and  Mr.  S.  W.  Burnham  announces  that 
he  has  detected  900  new  pairs.  Others  have  reported  perhaps  50  new  discoveries. 
This  makes  an  aggregate  of  4,450  double  stars. 

t  Zeta,  of  Hercules,  has  a  period  of  36  years ;  Eta,  of  the  Northern  Crown, 
a  period  of  43  years;  Zeta,  of  the  Crab,  59  years;  Xi,  of  the  Great  Bear,  63 
years.  Others  have  still  longer  periods  —  one  in  Virgo  being  513  years,  and  that 
of  Gamma,  of  the  Lion,  1,200  years, 


CONDITIONS   OF   THE    FIXED   STABS.  513 

I  believe  we  may  fairly  assume  that  such  planetary  attend- 
ants must  be  exceedingly  numerous.  It  seems  a  natural 
conjecture  that  all  these  luminous  attendants  of  other 
stars  are  planetary  or  derived  bodies  in  the  same  condi- 
tion as  once  characterized  the  earth,  and  more  recently, 
perhaps,  the  largest  planet  of  our  system.  "These 
planets,"  says  Secchi,  "  differ  from  ours  only  in  a  single 
point,  they  are  still  incandescent,  and  consequently  self- 
luminous."  • 

What  is  more  remarkable  and  interesting  is  the  fact 
that  many  stars  appear  triple  and  multiple.  Mr.  S.  W. 
Burnham  publishes  a  list  of  53  stars  enumerated  in  Struve's 
catalogue,  in  which  a  "closer  component"  has  been  more 
recently  discovered  —  the  majority  of  them  by  himself.* 
These  are  then  so  many  cases  of  stars  associated  in  groups 
as  high  as  triplets.  But  among  them  are  instances  in 
which  a  fourth,  fifth,  sixth  and  seventh  component  has 
been  detected.  Theta  of  Orion  is  a  celebrated  septuple 
star.  The  first  inference  which  one  feels  tempted  to  draw 
from  the  phenomena  of  triple  and  multiple  stars  is  the  ex- 
istence in  one  system,  of  more  than  one  planet  retaining  a 
self-luminous  condition.  It  might  be  suggested,  however, 
that  even  satellites  of  still  luminous  planets  may  retain 
the  luminous  condition.  In  this  case  we  should  ultimately 
detect  orbital  motion  around  one  of  the  components, 
together  with  motion  around  the  common  centre  of 
gravity  of  the  system.  This  is  an  interesting  inquiry  for 
astronomy,  f 

2.  Temporary  Stars. — From  time  to  time  during  cen- 
turies past,  stars  have  been  seen  to  burst  forth  into  lumi- 
nosity in  situations  before  unoccupied,  increase  in  bril- 

*S.  W.  Burnham,  Science,  ii,  35,  January  22,  1881. 

t  It  is  quite  possible  that  two  stars  under  the  combined  influence  of  mutual 
attraction  and  antecedent  motion,  not  approaching  sufficiently  near  for  coales- 
cence, should  enter  npon  orbital  revolutions  about  their  common  centre  of 
gravity. 

33 


514  FIXED   STARS   AXD   NEBULA. 

liancy  for  a  few  weeks  or  months,  and  then  gradually  wane, 
changing  from  white  to  yellow  and  red,  and  finally  disap- 
pearing. According  to  Humboldt,  twenty-one  such  stars 
were  recorded  during  the  interval  of  2,000  years  between 
134  B.C.  and  1848  A.D.  The  most  remarkable  of  these 
occured  in  1572  in  Cassiopreia,  and  was  specially  studied 
by  Tycho  Brahe.  It  exceeded  in  brilliancy  both  Sirius  and 
Jupiter.  Another  remarkable  occurrence  took  place  in 
1604,  in  Ophiucus,  and  was  studied  by  Kepler.  This  star 
nearly  equalled  Venus  in  brightness,  but  at  the  end  of 
fifteen  months  was  so  diminished  as  to  be  merely  a  tele- 
scopic object.  Another  was  discovered  by  Hind,  in  1848. 
The  one  which  occurred  in  May,  1866,  in  the  Northern 
Crown,  exceeded  the  second  magnitude  in  brightness. 

The  last  mentioned  was  spectroscopically  investigated. 
According  to  Huggins,  the  spectrum  indicated  two  dis- 
tinct sources  of  light,  each  producing  a  separate  spectrum. 
One  was  a  continuous  spectrum  crossed  by  dark  lines, 
similar  to  that  yielded  by  the  sun  and  most  of  the  stars. 
The  other  consisted  of  four  brilliantly  bright  lines.  The 
first  spectrum  showed  a  photosphere  of  incandescent  mat- 
ter either  solid  or  liquid,  surrounded  by  an  atmosphere  of 
cooler  vapors  giving  rise  by  absorption  to  the  dark  lines. 
The  other  spectrum  showed  the  presence  of  an  intensely 
luminous  gas  which,  according  to  Huggins,  was  appar- 
ently hydrogen  at  a  higher  temperature  than  existed  in 
the  photosphere  of  the  star.  These  spectral  phenomena 
have  prompted  the  suggestion  by  Huggins,  and  separately 
by  Rayet  and  Wolf,  that  the  sudden  brightness  of  the  star 
was  caused  by  an  outburst  of  intensely  heated  hydrogen 
gas,  which,  by  gradual  exhaustion,  occasioned  the  waning 
brilliancy  of  the  star.  Others  have  attributed  it  to  colli- 
sion with  some  other  orb;  but  this  idea  is  set  aside  by  the 
rapidity  of  the  decrease  in  brilliancy,  as  well  as  by  the 
supposed  periodicity  of  some  temporary  stars. 


CONDITIONS   OF  THE   FIXED   STARS.  515 

It  is  now  maintained  that  none  of  the  temporary  stars 
are  new  originations,  and  that  none  of  them  have  disap- 
peared from  existence,  if  even  from  visibility.  That 
occurring  in  the  Northern  Crown  is  still  telescopically 
visible;  and  it  is  maintained  that  the  new  stars  of  Tycho 
and  Kepler  may  still  be  seen.  In  fact,  the  belief  exists 
that  the  same  stars  had  previously  blazed  forth  more  than 
once  —  that  of  Tycho  in  945  and  1264,  and  that  of  Kepler 
in  393,  798  and  1203.  In  this  view,  temporary  stars  are 
only  variable  stars  with  very  long  periods.  But  this 
theory  needs  to  be  confirmed. 

I  think  these  phenomena  can  better  be  coordinated 
with  the  general  tenor  of  change  resulting  from  the 
genetic  development  of  cosmical  bodies.  As  every  cos- 
rnical  body  is,  in  one  stage  of  its  history,  thermallv  lumi- 
nous, and  at  another,  dark,  there  must  be  an  era  in  the 
lifetime  of  each  dark  body,  when  it  is  passing  from  the 
condition  of  a  luminous  to  that  of  a  darkened  body. 
There  must  be  many  stars  at  present  in  this  transitional 
stage.  There  must  be  many  more  which  have  served  as 
centres  of  planetary  motion,  but  have  since  cooled  to  a 
state  of  darkened  invisibility.  There  is  no  reason  to 
assume  that  most  stars  are  luminous.  It  is  probable  that 
space  is  strewn  with  planetized  suns  as  well  as  planets  and 
satellites.  There  are  as  many  stages  of  evolution  beyond 
the  luminous  stage  as  there  are  characteristic  of  it.  There 
must  be  many  dead  moons  lying  unburied  in  the  broad 
fields  of  space.  Indeed  we  may  conceive  immensity  like  the 
soil  on  which  human  races  tread,  to  be  more  densely  popu- 
lated by  the  dead  than  by  the  living.  We  dwell  in  a  cos- 
mic cemetery,  and  the  ashes  of  worlds  once  quick  with 
life  strew  the  pathways  of  the  burning  and  shining 
lights. 

There  are  three  ways,  under  this  conception  of  things, 
for  explaining  the  phenomena  of  a  temporary  star  —  or 


516  FIXED   STARS    AND    NEBULJE. 

one  which  bursts  forth  into  visibility  and  brilliancy  in  a 
new  place,  and  after  a  time  disappears: 

(1.)  Collision  of  a  precipitated  planet.  I  have  stated 
that  all  our  planets  must  be  tending  toward  precipitation 
on  our  sun.  It  may  be  that  after  our  sun  is  cooled  and 
darkened,  some  planet  will  yet  remain  to  be  reunited  with 
its  ancient  mother.  The  reunion  will  not  result  from  the 
direct  fall  of  the  planet  toward  the  sun,  but  from  a  spiral 
descent.  With  ever-increasing  velocity  the  planet  will 
approach  the  central  body,  and  will  finally  touch  it.  If 
both  bodies  are  solidified,  a  degree  of  friction  will  be 
developed  almost  exceeding  computation.  If  revolving 
wheels  sometimes  ignite  the  lubricating  substances  about 
their  axles,  what  will  occur  when  two  planets  crash  to- 
gether? The  solidity  of  the  rocks  will  seem  but  fluid. 
The  planets  will  melt  together  with  a  grinding,  crushing 
and  heat-developing  force  which  will  make  them  one,  and 
will  rekindle  their  extinguished  fires.  Fusion  and  even 
the  volatilization  of  portions  of  the  matter  must  be  the 
consequence.  To  an  observer  from  a  distant  planet  a  new 
star  would  appear.  Spectroscopically  examined,  its  light 
would  reveal  a  mixed  condition,  partly  fluid,  partly  vapor- 
ous; or  fluid  and  vaporous  alternately,  according  to  the 
varying  character  of  the  luminous  matter  turned  toward 
the  observer.  Such  phenomena  have  been  noted  in  con- 
nection with  the  temporary  star  which  appeared  in  the 
constellation  Cygnus  in  November,  1876.  An  objection 
to  this  mode  of  explaining  temporary  stars  lies  in  their 
brief  duration.  A  pair  of  united  worlds  thus  made  incan- 
descent would  require  ages  for  the  dissipation  of  their 
heat.  Such  an  event  would  rekindle  an  extinguished  star 
to  shine  permanently  during  human  epochs;  and  possibly 
some  of  our  stars  are  old  ones  thus  relighted.  It  is  still 
possible  that  the  precipitation  of  smaller  masses  of  mat- 


CONDITIONS   OF   THE   FIXED   STABS.  517 

ter  should  originate  incandescence  of  a  more  temporary 
character. 

(2.)  Eruptive  action  on  an  incrusting  globe.  In  all 
stages  of  our  earth's  incrusted  history,  the  disturbances 
of  the  crust  through  tidal  action  and  shrinkage  have 
opened  outlets  for  included  molten  matter.  Every  geo- 
logical period  has  been  marked  by  the  outflow  of  molten 
fluid,  to  some  extent.  But  the  largest  escapes  of  melted 
lava  have  taken  place  toward  the  close  of  the  Tertiary 
Age.  American  geologists  have  called  attention  to  the 
vast  extent  of  superficial  sheets  of  ancient  lava  on  our 
Pacific  slope;*  and  Professor  Geikie  has  collected  the 
evidences  of  a  similar  and  apparently  contemporaneous 
efflux  of  lava  over  northwestern  Europe,  and  regions 
since  covered  by  the  North  Sea  and  the  north  Atlantic. 
In  America  these  lava  sheets  spread  over  large  areas, 
ranging  from  the  valley  of  the  Columbia  River  to  Arizona 
and  New  Mexico,  and  as  far  east  as  the  Rio  Grande  of 
Texas.  In  some  places,  canons  four  thousand  feet  deep 
have  been  cut  through  by  subsequent  erosions.  Now,  it 
is  apparent  that  when  a  sheet  of  glowing  lava  was  spread 
rapidly  over  hundreds  of  thousands  of  square  miles,  the 
dark  planet  became  again  luminous  to  far  distant  observ- 
ers. An  enormous  evolution  of  gaseous  products  must 
have  accompanied  the  flow  of  the  lava.  The  luminous 
phenomena  must  have  endured  probably  for  some  weeks 
if  not  months;  but  the  length  of  the  period  of  luminosity 
could  not  have  approximated  that  resulting  from  the  pre- 
cipitation of  a  planetary  body.  Now,  if  an  ancient  dark- 
ened and  incrusted  sun  or  planet  should  undergo,  in  the 

*  See  especially  Jos.  Leconte,  On  the  Great  Lava  Flood  of  (he  West,  Amer. 
Jour.  Sci.,  III.  167-80,  259-67,  March  and  April,  1874.  See  also  J.  D.  Whitney: 
Geology  of  California,  and  the  various  Government  Geological  Reports.  There 
are  some,  also,  who  still  hold  to  the  primitive  molten  fluidity  of  all  granites  and 
many  ancient  «chists.  See  Address  of  C.  H.  Hitchcock  at  Minneapolis,  Science, 
ii,  223-7,  31  Aug.,  1883. 


518  FIXED    STARS   AND    NEBULAE. 

distant  heavens,  an  experience  similar  to  that  which  seems 
to  have  befallen  our  planet  in  the  later  stages  of  its 
history,  there  must  have  been  revealed  to  human  eyes  a 
spectacle  somewhat  similar  to  that  which  we  have  wit- 
nessed in  the  phenomena  of  "temporary  stars." 

(3.)  It  is  also  conceivable  that  a  rekindling  of  a  dark- 
ened sun  or  planet  should  result  from  the  impact  of  a 
wandering  cometary  body.  It  is  even  supposable  that 
a  luminous  star,  too  small  or  too  distant  to  be  visible, 
should  be  increased  in  brilliancy  by  such  a  collision  to  an 
extent  which  would  render  it  visible  to  human  eyes.  If, 
however,  so  great  an  increase  of  brilliancy  should  be 
caused  as  marks  the  usual  progress  of  a  temporary  star 
from  invisibility  to  a  star  of  first  magnitude,  there  would 
seem  to  be  implied  a  quantity  of  evolved  heat  which  could 
not  be  radiated  during  the  ordinary  continuance  of  a 
temporary  star. 

I  have  myself  adopted  the  second  explanation  as  the 
one  most  probable.  Every  cosmical  body  must  normally 
pass  through  the  incrustive  and  eruptive  stage  ;  but  we 
are  not  so  certain  that  every  one  is  destined  to  a  rekind- 
ling through  impact  of  descending  matter. 

3.  Variable  Stars. —  Those  stars  which  alternately  in- 
crease and  diminish  in  brilliancy  must  present  some  spe- 
cial conditions  admitting  of  correlation  with  the  progress 
of  cosmical  development.  More  than  twenty  of  them 
have  been  shown  to  possess  fixed  periods  of  change,  vary- 
ing from  about  two  days  and  twenty-one  hours  to  495 
days.*  Several  of  them  complete  their  periods  with  uni- 
formity reaching  to  a  minute,  and  even  a  second,  of  time. 
Nothing  but  axial  rotation  of  the  body,  or  orbital  revolu- 
tion of  an  occulting  body  is  conceivable  ^s  the  basis  of  such 
punctuality.  In  some  cases,  however,  as  in  that  of  Algol, 
the  period  is  too  short  to  ascribe,  with  probability,  to  oc- 

*Argelander,  in  Humboldt's  Cosmos,  iii. 


CONDITIONS   OF  THE   FIXED   STARS.  519 

cultations.  It  is  therefore  probable  that  the  phenomenon 
is  generally  due,  as  Zollner  suggested,  to  rotation  of  bod- 
ies having  sides  of  different  degrees  of  luminosity. 

But  there  is  also  a  variable  factor  in  the  periodicity  of 
most  variable  stars.  The  maxima  attained  are  not  always 
of  the  same  brightness ;  nor  are  the  minima  always  the 
same.  Sometimes  the  progress  toward  either  extreme  is 
marked  by  stages  more  or  less  irregular,  and  more  or  less 
differing  in  different  periods.  These  phenomena  point  to 
changes  in  the  brilliancy  of  the  light  received  from  the 
same  hemisphere.  It  is  highly  improbable  that  these 
irregular  fluctuations  are  caused  by  the  transit  of  dark 
bodies.  There  must  be  variations  in  the  intrinsic  lumi- 
nosity of  the  same  regions.* 

Now,  the  sun  is  a  star  near  enough  for  closer  study. 
The  sun's  disc  is  generally  mottled  by  the  well  known 
solar  spots.  The  number  of  spots  has  recently  been  shown 
to  increase  and  diminish  in  a  fixed  cycle  of  about  eleven 
years.  As  the  solar  light  must  be  somewhat  diminished 
by  the  presence  of  spots,  it  is  apparent  that  the  sun  has  a 
period  of  about  eleven  years.  It  is  not  at  all  improbable 
that  the  darkening  effect  of  the  spots  may  continue  to  in- 
crease until  the  diminution  of  light  at  times  of  greatest 
maculation  shall  become  distinctly,  marked.  With  the 
thickening  of  the  photospheric  envelope,  and  the  increase 
of  resistance  to  the  outbursts  of  the  internal  darker  gases, 
the  violence  of  the  action  accompanying  the  outbursts 
will  increase  ;  just  as  the  most  copious  outflows  of  lava 
on  the  earth's  surface  took  place  after  the  crust  had  be- 
come comparatively  rigid.  Our  sun  would  thus  be  un- 
questionably a  variable  star  ;  and  it  is  apparent  that  the 
initiatory  stage  of  such  a  condition  has  already  arrived. 
But  it  is  further  equally  conceivable  that  maculation  might 

*  On  the  causes  of  the  variability  of  stars  see  Pickering,  Proc.  Amer.  Acad. 
Arts  and  Sciences,  xvi. 


520  FIXED   STARS   AND    XEBULJE. 

constantly  predominate  on  one  side  during  one  or  two 
generations  of  men.  Such  a  condition  would  give  a 
shorter  period,  determined  by  the  sun's  axial  rotation. 
Or,  variations  in  the  depth  of  the  maculations  on  the 
brighter  or  the  darker  side  might  cause  irregular  progress 
toward  maximum  or  minimum  brightness.  These  consid- 
erations applied  to  the  variable  stars  of  our  firmament 
would  seem  to  offer  a  plausible  explanation  of  all  the 
phenomena. 

The  question  whether  the  variable  condition  attends 
upon  a  more  or  less  advanced  stage  than  that  presented 
in  stars  with  steady  light  can  only  be  answered  when  we 
know  the  cause  of  the  spots.  It  is  generally  admitted  at 
the  present  time,  that  their  existence  depends  on  the  out- 
burst, cooling  and  descent  of  heated  gaseous  matters  from 
the  region  within  the  solar  photosphere.  Father  Secchi, 
speaking  of  the  connection  between  the  spots  and  the 
protuberances,  says  :  "The  spot  is  formed  by  the  matter 
itself  which  the  eruption  projects  upon  the  solar  disc. 
The  dark  region  is  due  to  the  absorption  exerted  by  the 
vapors  issuing  from  the  bosom  of  the  sun  and  interposed 
between  the  observer  and  the  photosphere."*  The  theory 
of  Faye  differs  in  supposing  the  rupture  in  the  photo- 
sphere to  result  from  a  vortical  disturbance  in  that  layer, 
which  carries  cooler  vapors  down  ;  while  Professor  Young- 
favors  a  slight  modification  of  Secchi's  theory.  All  these 
views  make  the  spots  depend  on  the  superficial  accumula- 
tion of  vapors  relatively  cooler  than  the  photosphere  in 
whose  depressions  they  rest.  The  diminished  luminosity 
of  the  spots  is  due,  therefore,  to  the  high  absorptive  power 
of  their  substance  ;  and  this  results  from  a  relation  of 
temperature.  An  increased  efficiency  of  the  cause  or  con- 

*  Secchi:  Le  Soleil  2d  ed.  1875-7.  ii,  184.  See  also,  Faye,  Comptes  Rendus, 
Jan.  16  and  23, 1865,  and  July  27,  1869,  Tome  Ixviii,  p.  197;  Newcomb:  Popular 
Astronomy,  280-2:  Young:  The  Sun,  126,  175  ;  Langley,  in  Newcomb's  Popular 
Astronomy,  280-2. 


CONDITIONS   OF   THE   FIXED   STABS.  521 

dition  of  cooling  of  the  ejected  (or  accumulated)  vapors 
would  increase  the  maculation,  and  in  this  view,  one 
suggestion  would  be  that  excessive  maculation  marks  an 
advanced  stage  in  solar  life.  But  it  appears  that  macula- 
tion is  a  differential  phenomenon.  It  results  from  the  dif- 
ference in  the  temperature  of  the  subphotospheric  region 
and  the  region  exterior  to  the  photosphere  ;  and  this  could 
be  greatest  by  a  more  intensely  heated  interior  as  well  as 
by  a  cooler  condition  of  the  surrounding  atmosphere.  It 
was  the  opinion  of  Father  Secchi,*  nevertheless,  that 
maculation  is  a  phenomenon  of  advanced  solar  life,  and 
that  progressive  refrigeration  must  tend  to  increase  it. 
Should  this  be  a  true  conclusion,  our  sun  is  destined  to 
become  more  distinctly  a  variable  star  in  some  future  age  ; 
and  we  may  regard  such  stars  as  Beta  of  the  Lyre  and 
Mira  of  the  Whale  as  more  advanced  in  development  than 
our  own  sun  is.  This,  however,  is  a  question  which  must 
be  left,  for  the  present,  little  better  than  a  matter  of  con- 
jecture. Algol,  meantime,  which  varies  with  exact  regu- 
larity and  in  short  periods,  is  said  to  be  distinctly  a  star  of 
Secchi's  first  type  ;  and  is  to  be  associated,  therefore,  with 
Sirius  and  Vega.  Its  variability  I  have  thought  probably 
ascribable  to  rotation  of  a  body  of  different  luminosity  on 
different  sides. 

It  was  Zollner's  suggestion  that  a  variable  star  is  a  body 
reduced  to  a  liquid  state,  with  floating  slags  dimming  the 
light  on  certain  sides.  This  is  akin  to  my  suggestion  re- 
specting temporary  stars,  and  seems  a  very  rational  expla- 
nation. '  The  floating  slag,  however,  should  have  a  more 
fixed  position  than  can  be  conceived  probable  unless  nearly 
the  entire  surface  has  become  slag-covered.  This,  then, 
would  be  a  state  of  incipient  incrustation,  while  the  tem- 
porary star  would  exemplify  an  incident  in  advanced  in- 
crustation. 

*  Secchi :  Le  Soleil,  ii,  456. 


522  FIXED   STARS  AND   NEBULA. 

4.  Gradations  of  Stars. — Every  one  has  remarked  the 
fact  that  certain  stars,  like  Sirius,  shine  with  a  white  light; 
others,  like  Capella,  with  a  yellow  light,  and  still  a  few 
others,  with  a  ruddy  light.  Father  Secchi  showed  that 
these  three  classes  of  stars  afford  three  classes  of  spectra. 
As  the  spectrum  depends  on  conditions  of  existence  of  a 
source  of  light,  in  reference  to  temperature,  envelopes 
and  pressure,  the  variously  colored  stars  must  exist  in  dif- 
ferent conditions.  In  order  to  learn  how  far  the  spectro- 
scopic  characters  of  the  stars  furnish  data  for  coordinating 
them  in  a  genetic  series,  I  present  a  condensed  statement 
of  the  characteristics  of  the  four  or  five  classes  of  stars 
pointed  out  by  Father  Secchi*  in  his  beautiful  work  on 
the  sun. 

First  Type. — This  embraces  most  of  the  white  stars, 
such  as  Vega,  Altai'r,  Regulus,  Rigel,  the  stars  of  the 
Great  Bear  with  the  exception  of  a,  those  of  Serpentarius, 
etc.  The  class  includes  about  half  of  the  stars.  Though 
commonly  called  white,  they  are,  in  reality,  faintly  blue. 
The  remarkable  variable  star  Algol  seems  to  belong  here. 
The  spectrum  in  this  class  presents  a  group  of  seven  colors 
interrupted  by  four  dark  lines,  one  in  the  red,  another  in 
the  green-blue  and  two  in  the  violet.  These  all  belong  to 
hydrogen,  and  coincide  with  the  four  brightest  lines  of 
this  gas,  when  existing  at  a  high  temperature.  Besides 
these  broad  fundamental  lines,  the  brightest  of  these  stars 
afford  a  very  fine  dark  line  in  the  yellow,  which  appears 
to  coincide  with  sodium;  and  in  the  green,  some  still 
fainter  lines  which  pertain  to  magnesium  and  iron.  The 
most  striking  peculiarity  of  this  type  of  stars  is  the  breadth 
of  the  hydrogen  lines;  which  tends  to  show  that  the  ab- 

*  Secchi:  Le  Soleil,  2d  ed.,  ii,  449-61;  first  announced  in  1867,  in  Catalogo 
delle  Stelle  dl  cui  si  t  determinate  lo  Spet/ro  luminoso  ali'  ossercatoiio  del  Col- 
tegioRoina.no.  See  the  substance  of  Father  Secchi's  views  in  Schellen:  Die 
Spectralana/yse,  and  the  English  translation,  Am.  ed.,  Spectral  Analysis,  342-50. 


CO^DITIO^S   OF   THE   FIXED   STAES.  523 

sorbent  layer  possesses  great  thickness  and  exists  under 
considerable  pressure. 

Second  Type. — This  embraces  the  yellow  stars,  like 
Capella,  Pollux,  Arcturus,  Aldebaran,  Alpha  of  the  Great 
Bear,  Procyon,  etc.  Arcturus,  however,  approaches  the 
third  type,  while  Procyon  approaches  the  first.  The  spec- 
trum is  perfectly  similar  to  that  of  the  sun.  This  class 
embraces  about  one-third  of  all  the  stars. 

Third  Type. — These  stars  are  all  variable.  In  color 
they  range  from  red  toward  orange.  The  type  includes 
Alpha  of  Hercules;  Beta  of  Pegasus;  Omicron  (or  Mira) 
of  the  Whale;  Alpha  of  Orion;  Antares,  etc.  There  are 
about  thirty  of  first  importance,  and  one  hundred  in  all. 
The  fundamental  dark  lines  are  the  same  as  in  the  second 
type,  but  there  are  also  present  numerous  nebulous  bands 
which  divide  the  spectrum  and  make  of  it  a  sort  of  colon- 
nade illuminated  from  the  side  of  the  red.  These  spectral 
zones  depend  on  variations  in  the  stars,  and  these  depend 
on  the  more  or  less  absorbent  action  of  their  atmospheres. 
At  the  bottom  of  the  solar  spots  a  spectrum  is  obtained 
more  profoundly  rayed,  and  crossed  also  by  dark  bands. 
These  stars  then  appear  to  owe  their  spectrum  to  an  ab- 
sorption analogous  to  that  produced  in  the  solar  spots.  If, 
therefore,  our  sun  had  everywhere  an  absorbent  layer  like 
that  exposed  in  the  spots,  it  would  present  the  same  aspect 
as  the  stars  of  this  class.  The  most  conspicuous  lines  are 
those  of  magnesium,  sodium  and  iron.  They  are  rather 
bands  than  lines,  since  they  are  broad,  and  shaded  along 
the  edges.  This  seems  to  indicate  a  powerfully  absorptive 
atmosphere.  There  are  also  fine  hydrogen  lines,  but  they 
do  not  dominate  as  in  the  first  two  types.  This  gas  cer- 
tainly exists  in  these  stars,  but  its  lines  are  partially  re- 
versed, as  happens  in  the  spectrum  of  the  solar  spots. 
Most  of  the  dominant  lines  belong  to  metals  which  have 
been  found  in  the  sun. 


524  FIXED   STARS   AND   NEBULA. 

The  spectrum  is  the  same  as  that  of  the  sun  —  or 
rather  Arcturus — but  profoundly  divided  by  nebulous 
lines  due  probably  to  oxides.  This  indicates  a  tempera- 
ture less  than  that  of  the  sun. 

The  stars  of  the  second  and  third  types  seem  to  differ 
simply  in  the  thickness  of  their  atmospheres,  and  in  the 
discontinuity  of  the  photosphere  in  the  third  type.  These 
should  have,  then,  variable  spots  like  those  of  the  sun,  but 
of  vastly  greater  dimensions,  or  even  completely  envelop- 
ing the  star,  forming  a  general  layer  more  absorbent  and 
less  heated. 

Fourth  Type. — This  consists  of  about  thirty  stars  of 
blood-red  color.  The  spectrum  contains  three  fundamen- 
tal bright  bands,  yellow,  green  and  blue,  not  reducible 
to  the  preceding  type,  for  the  distribution  of  the  light 
is  entirely  different.  They  are  brightest  on  the  side 
toward  the  violet,  and  fade  gradually  in  the  opposite 
direction.  Some  yield  a  faint  trace  of  red.  Some  of  the 
dark  lines  coincide  pretty  well  with  the  third  type,  but 
the  spectrum  as  a  whole  is  that  of  a  gaseous  bodv  rather 
than  one  of  absorption.  If  considered  an  absorption 
spectrum,  it  presents  the  characteristics  of  carbon  com- 
pounds, such  as  are  yielded  when  a  succession  of  electric 
sparks  is  passed  through  vapor  of  benzine  and  atmos- 
pheric air. 

Fifth  Type. — This  consists  of  few  stars,  including 
Gamma  of  Cassiopceia  and  Beta  of  the  Lyre,  a  variable 
star.  It  affords  a  direct  hydrogen  spectrum.  The  first 
named,  according  to  Huggins,  gives  a  spectrum  in  which 
the  bright  lines  Ha  (red)  and  H  ft  (greenish  blue)  are  visi- 
ble in  the  places  of  the  dark  lines  C  and  F.  A  bright 
line  in  the  yellow,  in  place  of  D,  is  also  suspected.  The 
star  Eta  Argus  gave  a  spectrum  also,  in  which  some  of 
the  most  intense  of  the  nitrogen  lines  were  seen  as  bright 
lines.  Two  variable  stars  have  been  seen  to  give  also  a 


CONDITIONS    OF   THE   FIXED    STAKS.  525 

direct  but  discontinuous  spectrum — one  in  1866,  in  the 
Northern  Crown;  the  other  R  Geminorum.  The  tempo- 
rary star  in  the  Swan  had  also  a  similar  spectrum.  It 
seems,  according  to  Secchi,  to  imply  a  rapid  combustion 
at  some  former  epoch  —  the  light,  probably,  having  been 
many  years  in  reaching  us. 

The  stars  in  the  constellation  Orion  present  still  other 
peculiarities.  They  belong  to  the  second  type  in  the  ex- 
treme fineness  of  the  lines,  but  are  quite  exceptional  in 
the  nearly  complete  absence  of  the  red  and  yellow.  All 
the  stars  of  this  region  present  a  double  character:  (1) 
They  have  a  very  pronounced  green  tint.  (2)  Their  spec- 
tral lines  are  so  fine  that  it«is  difficult  to  separate  them. 
On  the  contrary,  the  region  of  the  Whale  and  the  Po 
contains  a  very  large  number  of  yellow  stars.  This  dis- 
tribution, says  Secchi,  cannot  exist  by  chance.  It  de- 
pends, undoubtedly,  on  the  nature  and  the  state  of  the 
substances  which  fill  different  parts  of  the  universe. 

No  inherent  improbability  exists  that  the  distribution 
of  the  different  substances  is  somewhat  different  in  regions 
remote  from  each  other.  But  we  know  too  much  of  the 
uniformities  pervading  the  widest  regions  of  space  to 
believe  that  differences  of  substance  can  produce  any 
fundamental  peculiarities  such  as  characterize  the  various 
types  of  stars.  These  peculiarities,  in  all  probability, 
arise  from  different  conditions  of  the  common  substance. 
There  are  contrasts  of  condition,  therefore,  corresponding 
to  the  colors  of  the  stars.  Whether  the  different  con- 
ditions are  successive  in  the  progress  of  a  cosmical  evolu- 
tion is  an  unsolved  problem.  It  may  be  noted,  however, 
that  the  series  of  colors,  white,  yellow  and  red,  is  a  suc- 
cession presented  by  successive  stages  of  cooling  from  a 
white  heat.  Still,  these  stages  as  observed,  occur  in  the 
cooling  of  a  body  whose  temperature  is  low  enough  to 
permit  it  to  retain  a  solid  condition  from  the  first  to  the 


526  FIXED    STARS   AKE>   NEBULA. 

last;  while  suns,  in  all  their  luminous  stages,  are  supposed 
-to  be  vastly  hotter  than  white-hot  iron.  Would  this  suc- 
cession of  colors  be  presented  in  stages  of  cooling,  all  of 
which  are  far  above  the  temperatures  of  molten  iron?  Or, 
is  the  supposition  erroneous  that  all  the  stellar  matter 
determining  the  color  of  the  light  is  so  intensely  heated? 
There  is  a  time  in  the  history  of  a  sun  when  intense 
heat  has  resulted  from  the  gravitational  condensation  of 
its  parts.  Most  of  its  substance  exists  in  a  gaseous  or 
even  dissociated  condition.  It  is  improbable  that  a  high 
degree  of  luminosity  characterizes  such  matter.  But  the 
peripheral  region  must  always  experience  important 
effects  from  radiation.  It  seems  very  improbable  that  the 
general  temperature  of  the  mass  could  be  so  high  or  so  uni- 
versally distributed  that  the  surface  should  not  be  chilled 
to  the  point  of  formation  of  fire  mist.  A  zone  of  fire  mist 
would  envelop  the  gaseous  globe  like  a  skin.  Fire  mist 
is  simply  gas  cooled  till  minute  liquid  particles  come  into 
existence  which  float  in  a  common  atmosphere  of  gases 
not  yet  condensed.  In  the  liquid  or  solid  state,  lumi- 
nosity is  greatly  increased,  even  at  a  lower  temperature. 
In  such  a  zone  of  fire  mist,  a  circulation  of  particles  must 
be  in  active  progress  Coalescence  of  particles,  as  in  a 
cloud  of  aqueous  vapor,  would  give  rise  to  drops  which 
would  descend  like  rain  to  the  lower  surface  of  the  photo- 
spheric  fire  mist.  They  would  even  penetrate  the  hotter, 
gaseous  nucleus  for  a  limited  distance,  but  would  soon  be 
dissolved  to  gas  and  returned  to  the  zone  of  the  fire  mist. 
By  this  process,  long  continued,  this  photosphere  would 
be  deepened,  and  the  nucleus  correspondingly  diminished 
in  volume.  In  the  course  of  time,  the  nucleus  would  be 
wholly  replaced  by  fire  mist ;  and  then  would  begin  that 
central  accumulation  of  a  liquid  core  of  which  I  have  else- 
where spoken.  The  proper  life  of  a  sun  is  therefore  divided 
into  two  stages,  in  the  first  of  which  a  gaseous  nucleus 


CONDITIONS   OF   THE   FIXED   STAES.  527 

goes  on  diminishing,  and  in  the  other  of  which  a  molten 
nucleus  goes  on  increasing. 

But  in  either  stage,  the  photospheric  zone  is  reduced  to 
the  point  of  liquefaction  of  a  considerable  proportion  of 
its  substance.  Being  liquefied,  its  temperature  must  be 
such  as  is  compatible  with  the  existence  of  matter  in  that 
state.  According  to  this  reasoning,  the  condition  of  the 
photospheric  particles  might  be  compared  with  that  of  a 
mist  of  molten  iron.  It  might  possess  the  temperature 
and  the  luminosity  which  belong  to  terrestrial  substances 
at  the  temperature  of  a  white  heat.  The  deeper  portions 
of  the  photosphere,  however,  must  be  more  copiously  per- 
vaded by  a  gaseous  medium  at  a  higher  temperature;  and 
the  entire  gaseous  nucleus,  so  far  as  I  perceive,  may  sub- 
sist at  any  temperature  compatible  with  the  evidences 
bearing  on  the  intrinsic  heat  of  solar  bodies. 

But  if  the  particles  upon  the  outer  surface  of  a  photo- 
sphere may  exist  at  the  temperature  of  the  white  heat  of 
molten  iron,  it  seems  possible  they  may  also  exist  as  solid 
particles  at  the  lower  temperature  which  emits  a  yellow, 
or  even  a  ruddy,  light.  In  this  view,  the  colors  of  the 
stars  may  truly  denote  successive  stages  in  a  process  of 
cooling.  Whether  such  a  conclusion  is  compatible  with 
the  evidences  on  which  scientific  opinion  has  generally 
agreed  to  ascribe  a  much  higher  temperature  to  the  sur- 
face of  the  sun,  is  a  question  for  the  future  to  decide. 
It  will  be  noticed,  however,  that  the  general  heat  of  the 
solar  surface  is  constituted  partly  by  the  higher  tempera- 
ture of  the  gaseous  medium  from  which  the  photospheric 
particles  are  generated.  This  may  also  be  added,  that  on 
most  of  the  solar  bodies  the  enormous  force  of  gravity 
would  have  the  effect  of  raising  the  point  of  liquefaction 
from  a  gas,  and  the  enormous  pressure  of  the  superin- 
cumbent atmosphere,  however  rarefied  by  heat,  would  in- 
crease this  effect;  so  that  the  incipient  molten  stage 


528  FIXED   STARS  AND   NEBULAE. 

would  imply  a  higher  absolute  temperature  than  on  the 
earth.  It  is  still  true  that  the  lower  limit  of  luminosity, 
and  probably  all  higher  degrees  of  it,  would  be  deter- 
mined by  the  rate  of  molecular  vibration,  independently 
of  the  condition  of  the  matter  as  to  fluidity.  For  this 
reason  nearly  all  substances  might  require  an  intense 
white  heat  even  for  liquefaction,  and  a  vastly  higher  heat 
for  conversion  into  the  less  luminous  condition  of  gaseity. 

In  view  of  the  whole  range  of  considerations,  I  shall 
assume  provisionally  that  the  various  colors  of  the  stars 
exhibit  a  gradation  in  the  cooling  process. 

A  few  further  obvious  suggestions  may  be  made  in  this 
connection.  In  the  earliest  stages  of  photospheric  exist- 
ence, the  fire-mist  film  would  be  so  thin  as  to  possess 
a  lower  degree  of  luminosity  than  at  a  later  stage.  The 
light  emitted  would  be  thin  and  leaden  in  hue.  It  is 
quite  conceivable,  also,  that  causes  may  exist  in  particular 
cases,  for  changes  in  the  hue  of  the  light  resulting  from 
diminished,  as  well  as  increased,  depth  of  the  photo- 
spheric  zone.  A  star,  at  one  time  yellow,  might  recede  to 
the  white  stage.  A  white  star  might  recede  to  the  bluish 
or  leaden  stage  by  increase  of  its  general  temperature. 
Thus,  it  is  possible  the  reputed  changes  in  the  colors  of 
certain  stars,  which  are  of  a  retrogressive  significance, 
mav  be  interpreted  in  harmony  with  the  provisional  con- 
clusion which  I  have  enunciated  respecting  the  meaning 
of  color  gradation  among  the  stars. 

But,  if  we  admit  that  the  white,  yellow  and  red  colors 
of  the  stars  represent  as  a  general,  though  not  invariable 
rule,  successive  cooling  stages,  it  remains  to  ascertain 
whether  these  stages  all  appertain  to  photospheric  life,  or 
characterize,  in  part,  the  later  stage,  incandescent  incrus- 
tation; and  also,  whether,  if  one  or  all  of  them  apper- 
tain to  photospheric  life,  it  is  that  period  which  precedes 
or  follows  the  beginning  of  liquid  nucleation.  We  dis- 


CONDITIONS    OF   THE   FIXED    STARS.  529 

tinguish  three  phases  in  the  life  of  a  self-luminous  cosrni- 
cal  globe:  (1)  The  gaseous-nuclear  phase;  (2)  the  liquid- 
nuclear  phase;  (3)  the  incrusted  phase.  During  the  first 
two,  or  characteristically  solar,  phases,  a  photosphere 
exists,  consisting  of  particles  of  liquid  or  solid  matter, 
and  giving  by  itself  a  continuous  spectrum;  but  an  ab- 
sorbent atmosphere  still  existing  in  abundance,  the  result- 
ant spectrum  is  crossed  by  dark  lines.  The  volume  and 
density  of  the  enveloping  atmosphere  are  so  great  that 
the  dark  lines  possess  a  greater  breadth  than  in  the  solar 
spectrum.  During  the  third  phase,  the  spectrum  should 
be  continuous;  but  still,  at  the  supposed  temperature,  a 
dense,  heterogeneous  and  absorbent  atmosphere  might 
still  impress  dark  lines  upon  the  bright  continuous  spec- 
trum. Now,  the  spectral  conditions  of  the  first  two  stages 
are  exhibited  by  the  white  and  yellow  stars  —  the  white 
stars  giving  the  broadest  dark  lines,  and  thus  evincing  the 
greatest  depth  of  atmosphere.  We  must  conclude  that 
these  two  stages  belong  to  the  photospheric  period.  The 
indications  of  the  few  red  stars  are  ambiguous.  Their 
spectrum  is  characterized  by  dark  lines,  but  Father  Secchi 
was  of  the  opinion  that  they  offer  some  indications  of 
more  predominant  gaseity  than  the  others.  Their  red 
color  may  result  from  some  other  cause  than  their  ad- 
vanced stage  of  cooling.  But  since  the  incrusted  state 
must  be  accompanied  still  by  a  voluminous  envelope  of 
gases,  and  since  ruddy  light  is  certainly  expressive  of 
diminished  incandescence,  while  further,  the  light  of  the 
crust,  with  diminished  intensity,  would  be  less  able  to 
contend  with  the  absorbent  and  luminous  powers  of  the 
atmosphere,  I  shall  venture  to  assume,  though  provision- 
ally, as  before,  that  the  ruddy  stage  is  generally  to  be 
interpreted  as  the  early  incrusted  phase. 

The  variable  ruddy  stars  will  represent  earlier  phases  — 
sometimes  an  advanced  macular  condition,  and  in  some 


530  FIXED    STARS    AN"D   XEBUL^S. 

cases  a  phase  of  incipient  incrustation;  while  the  tem- 
porary stars  are  phenomena  of  advanced  incrustation. 

5.  Indications  of  Incipient  Stellation. —  Certain  phe- 
nomena presented  by  celestial  objects  not  recognized  as 
well  formed  stars  may  be  interpreted  as  characteristics  of 
incipient  stellation.  Certain  dense  star  clusters,  as  well 
as  most  of  the  so-called  resolvable  nebulae,  present  con- 
tinuous spectra.  Such  a  spectrum  is  yielded  by  incandes- 
cent solid  or  liquid  bodies.  When  such  a  body  is  sur- 
rounded by  gases  of  lower  temperature,  dark  absorption 
lines  appear  in  the  spectrum;  but  if  the  surrounding  gas 
itself  is  intensely  heated,  it  imparts  its  own  bright  lines 
to  the  spectrum,  and  these  then  appear  superposed  over 
a  continuous  spectrum.  But  there  is  a  certain  intermedi- 
ate state  of  luminosity  in  the  envelope  in  which  its 
absorbent  power  is  just  neutralized  by  its  emissive  power, 
and  its  effect  on  the  spectrum  of  the  inclosed  molten 
material  disappears.  Such  seems  to  be  the  condition  •  of 
the  gaseous  medium  in  the  star  clusters  and  resolvable 
nebuljB  referred  to. 

At  an  earlier  stage,  the  emissive  property  of  the  heated 
atmosphere  preponderates,  and  the  spectrum  is  one  of 
bright  lines  over  a  continuous  spectrum.  The  preponder- 
ance in  the  emissive  power  of  the  gaseous  medium  may 
depend  on  the  relatively  low  temperature  of  the  enveloped 
portions;  and  this  may  depend  on  the  comparatively  low 
degree  of  condensation  as  yet  attained.  A  later  period, 
therefore,  would  witness  a  greater  degree  of  condensation, 
intenser  central  heat,  and  a  relatively  more  powerful  lumi- 
nosity. That  is,  a  more  advanced  stage  would  increase 
the  amount  of  fire  mist  and  its  relative  luminosity,  besides 
reducing  the  volume  and  pressure  of  the  envelope,  and 
thus  establish  those  relations  which  produce  a  continuous 
spectrum  crossed  by  the  dark  lines  of  an  absorbent  me- 
dium. This  description  of  spectral  power  is  possessed  by 


COSMOGOHTIC    COXDITIOXS   OF    NEBULA.  531 

"Planetary  Nebulae"  and  "Nebulous  Stars."  We  may, 
therefore,  unite  with  Sir  William  Herschel  in  considering 
these  forms  as  stages  of  cosmical  development,  showing  a 
passage  from  nebular  to  stellar  life. 

§  2.   COSMOGONIC  CONDITIONS  OF  NEBULAE. 

Le  monde  s'elargit  done  a  nos  yeux;  le  systeme  solaire  ne  nous  parait  phis 
que  comme  un  point  dans  1'espace.  Quelle  difference  entre  ces  idees  si  larges 
et  celles  qui  autrefois  limitaient  le  monde  an  notre  globe.  *  *  *  II  est  prob- 
able que  la  re'union  des  grands  6toiles  qui  environnent  notre  Soleil  n'est  qu'un 
des  amas  qui  forment  la  Voie  lactee,  et  que  vu  d'une  certaine  distance,  cct  ainas 
apparaitrait  comme  une  tache  plus  blanche  dans  la  Voie  lactee  elle-meme.— 
SECCHI. 

The  typical  nebula  is  one  which  is  irresolvable  and 
shines  with  a  faint  light,  affording  a  spectrum  of  one  or 
more  bright  lines.  The  brightest  of  these  lines,  with  a 
wave  length  of  5,005,  is  coincident  with  a  nitrogen  line. 
The  second,  when  others  exist,  has  a  wave  length  of  4,957 
(Angstrom).  The  other  two  are  coincident  with  hydrogen 
lines  H  /?  or  F  and  H  f  near  G.  This  spectrum  is  some- 
times superposed  on  a  faint  continuous  spectrum. 

In  some  careful  investigations  recently  made  upon  the 
nebula  in  Orion  by  Mr.  Huggins*  a  fifth  relatively  strong 
line  was  observed  in  the  ultra-violet,  of  wave  length  3,730, 
which  appeared  to  correspond  to  £  in  the  typical  spectrum 
of  white  stars. f  Mr.  Huggins  states,  also,  that  he  cannot 
say  positively  that  the  hydrogen  lines  between  Hy  and 
the  fifth  nebular  line  are  wanting,  and  he  even  suspects 
their  presence,  as  also  others  beyond  the  fifth  nebular  line. 
Mr.  Huggins  further  says,  that  outside  of  the  usual 
stronger  continuous  spectrum,  which  he  attributes  to  stel- 
lar light,  he  suspects  an  exceedingly  faint  trace  of  a  con- 
tinuous spectrum.  Dr.  Draper's  photographs  show  also  a 
continuous  spectrum  from  two  condensed  portions  just 

*  Proc,  Roy,  Soc.,  March  16,  18S3,  Xature,  xxv,  489. 
t  Phil.  Trans.,  1880,  p.  677, 


532  FIXED   STARS   AND    NEBULA. 

• 

preceding  the  trapezium.  These  observations  show  the 
nebular  spectrum  to  be  less  simple  than  had  been  supposed, 
and  demonstrate,  apparently,  the  presence  at  least  of 
hydrogen  and  nitrogen.  Frankland  and  Lockyer  have 
shown  that  the  spectrum  indicates  a  lower  temperature 
than  exists  in  our  sun,  and  a  remarkably  low  density. 

The  presence  of  bright  lines  indicates  that  an  important 
portion  of  the  nebula  is  gaseous,  while  the  faint  contin- 
uous spectrum,  when  present,  seems  to  indicate  the  exist- 
ence of  incandescent  solid  or  liquid  matter.  Though  Mr. 
Huggins,  an  eminent  authority,  inclines  to  attribute  the 
continuous  spectrum  to  stellar  light,  I  see  no  strong  rea- 
son in  the  phenomena  for  denying  that  both  solid  and 
liquid  matter  exist  in  a  luminous  condition  in  most  nebula?. 
Assuming,  as  I  have  done,  that  nebular  history  begins 
with  the  aggregation  of  cold  matter,  some  of  which  is 
analogous  to  that  forming  meteoroidal  trains,  there  would 
naturally  arrive  a  time  when,  by  collision  of  hard  constit- 
uents, and  condensation  of  gaseous  constituents,  heat 
would  be  developed.  This  would  sooner  or  later  originate 
gaseous  luminosity;  and  this  is  the  typical  condition. 
But  from  this,  by  peripheral  condensation,  must  arise  some 
amount  of  fire  mist;  and  the  very  process  of  volatilization 
implies  also  a  stage  of  fusion  passed.  This  fire  mist,  and 
this  antecedent  liquidity  would  afford  the  continuous  spec- 
trum. The  double  spectrum  is  shown  not  only  in  some 
continuous  nebulae,  but  also  in  a  small  number  of  nebulous 
stars.  Some  nebula?,  as  heretofore  stated,  seem  to  undergo 
a  process  of  segregation  of  parts  by  curdling  and  accumu- 
lation apparently  around  nuclei.  They  become  then  clus- 
ters of  nebulous  stars.  Certain  so-called  resolvable  nebula? 
present  this  condition.  This  seems  rather  a  collateral 
than  a  consecutive  phase,  since,  as  I  have  before  indicated, 
it  may  be  regarded  as  characterizing  nebula?  which  do  not 
rotate  and  annulate. 


COSMOGONIC    CONDITIONS    OF   NEBULA.  533 

Finally,  we  have  to  consider  a  prenebular  stage.  Be- 
fore the  matter  of  the  nebula  is  collected  in  form  it  must 
exist  in  a  formless  or  chaotic  stage.  I  have  already  de- 
scribed the  phenomena  which  I  suppose  to  be  connected 
with  prenebular  conditions.  The  matter  is  diffused;  it  is 
cold;  it  is  composed  of  mineral  substances  aggregated  in 
masses,  at  least  in  part,  which  are  drawn  together  by 
mutual  attractions,  forming  distinct  groups  or  swarms 
which  are  further  aggregated  successively,  until  those  vast 
fields  of  cosmical  stuff  are  accumulated  which  become 
luminous  nebulae.*  Perhaps  generally  the  aggregation 
into  masses  is  very  limited,  and  the  matter  exists  mostly 
as  widely  scattered  particles  or  molecules.  This  diffused 
and  unorganized  condition  of  primitive  world  stuff  answers 
to  the  chaos  conceived  by  Kant,  though  he  banished  it 
from  the  realm  in  which  cosmical  organization  has  taken 
place,  while  the  present  conception  supplies  all  the  spaces 
in  the  midst  of  the  worlds  with  these  seeds  of  cosmical 
organization. 

I  am  not  aware  that  it  is  possible  to  trace  inductively 
the  history  of  world  formation  to  any  remoter  point.  It 
is  certainly  possible  to  conceive  these  cosmical  atoms  as 
arising  out  of  some  transformation  of  the  ethereal  medium, 
and  more  than  once  expression  has  been  given  to  such  a 
speculation. f  But  we  know  too  little  of  the  nature  of 
ether  to  ground  a  scientific  inference  of  this  kind;  and  we 
certainly  have  no  knowledge  or  conception  of  any  con- 
dition of  matter  antecedent  to  that  in  which  it  possesses 
resistance,  weight  and  inertia.  The  attempt  to  go  farther 
involves  us  in  speculations  of  a  metaphysical  character 
respecting  the  ultimate  nature  of  matter,  and  this  is  a  field 
of  inquiry  which  it  is  not  proposed  to  enter. 

*  See  more  specifically.  Part  I,  ch.  i,  §  7. 

t  See  the  references  pp.  49,  50,  61.  A  later  article  by  A.  S.  Herschel  appears 
in  Nature,  xxviii,  294-7,  July  26,  1883. 


CHAPTER  II. 

THE   COSMIC   CYCLE. 

Facies  totius  Universi,  quamvis  inflnitis  modis  variet,  manet  tamen  semper 
eadem.— SPINOZA. 

Herschel,  en  observant  leg  nebuleuscs  an  moyen  de  ses  puissans  telescopes,  a 
suivi  les  progres  de  leur  condensation  non  snr  une  seule,  ces  progres  ne  ponvaut 
devenir  sensibles  pour  nous,  qu'  apres  des  siecles;  mais  sur  leur  ensemble, 
comme  on  suit  dans  une  vaste  foret  I'accroissement  des  arbres,  sur  les  indi- 
vidus  de  diverges  ages,  qu'elle  renferme. —  LAPLACE. 

§  1.     THE  KEYS  OF  COMPARATIVE  GEOLOGY. 

THE  views  presented  in  the  foregoing1  chapters  direct 
attention  to  some  of  the  sublimest  considerations 
which  can  occupy  the  human  mind.  We  rise  from  the 
contemplation  of  the  interests  and  affairs  of  the  indi- 
vidual or  of  the  human  race,  not  alone  to  that  larger 
scope  of  events  which  constitutes  the  lifetime  of  the 
habitable  globe  which  endures  while  generations  and  na- 
tionalities come  and  disappear;  but  that  grander  concep- 
tion of  the  cycle  of  events  which  constitutes  the  round  of 
evolutions  awaiting  every  aggregation  of  cosmic  matter 
in  the  material  universe.  I  wish  to  impress  this  thought 
of  the  unity  of  cosmical  history,  and  lead  my  reader  to 
an  impressive  apprehension  of  the  vastness  of  the  scheme 
to  which  he  belongs,  and  of  the  exaltation  of  constituting 
a  part  of  a  scheme  so  vast. 

The  possibility  of  rising-  to  a  comprehension  of  a  sys- 
tem of  coordination  so  far  outreaching  in  time  and  space 
all  range  of  human  observation,  is  a  circumstance  which 
signalizes  the  power  of  man  to  transcend  the  limitations 
of  changing  and  inconstant  matter,  and  assert  his  superi- 

534 


THE   KEYS   OF   COMPARATIVE   GEOLOGY.  535 

ority  over  all  insentient  and  perishable  forms  of  being. 
There  is  method  in  the  succession  of  events,  and  in  the 
relation  of  coexistent  things,  which  the  mind  of  man 
seizes  hold  of;  and  by  means  of  this  as  a  clew,  he  runs 
back  or  forward  over  aeons  of  material  history  of  which 
human  experience  can  never  testify.  Events  germinate 
and  unfold.  They  have  a  past  which  is  connected  with 
their  present,  and  we  feel  a  well  justified  confidence  that 
a  future  is  appointed  which  will  be  similarly  connected 
with  the  present  and  the  past.  This  continuity  and  unity 
of  history  repeat  themselves  before  our  eyes  in  all  con- 
ceivable stages  of  progress.  The  phenomena  furnish  us 
the  grounds  for  the  generalization  of  two  laws  which  are 
truly  principles  of  scientific  divination,  by  which  alone 
the  human  mind  penetrates  the  sealed  records  of  the  past 
and  the  unopened  pages  of  the  future.  The  first  of  these 
is  the  law  of  evolution,  or,  to  phrase  it  for  our  purpose, 
the  laic  of  correlated  successiveness  or  organized  history 
in  the  individual,  illustrated  in  the  changing  phases  of 
every  single  maturing  svstem  of  results;  as  organic  struc- 
ture, human  civilization  or  world-growth.  The  second  is  the 
law  of  correlated  simidtaneousness,  or  parallel  history  in 
many  individuals,  whereby  many  particular  instances  of 
progressive  development  in  different  stages  of  maturity 
are  presented  simultaneously;  as  the  different  persons  in 
a  large  city  exemplify  simultaneously  the  stages  of  devel- 
opment attained  by  any  individual  on  every  day  of  his  life. 
Thus,  by  Virtue  of  these  two  laws,  each  individual  under- 
going an  evolution  finds  at  every  moment  its  entire  past  and 
future  recorded  in  the  present  of  other  individuals  belong- 
ing in  the  same  category.  The  man  of  mature  years  can 
turn  in  one  direction  and  study  the  stages  which  he  has 
passed  through  from  earliest  infancy;  and  in  the  other  di- 
rection, the  stages  which,  in  the  course  of  nature,  he  will 
pass  through  to  remotest  old  age.  I  go  into  the  forest,  and 


536  THE   COSMIC    CYCLE. 

within  an  hour  trace  the  life  history  of  an  oak  all  the  way 
from  the  acorn  to  the  crumbling  veteran  of  three  hundred 
years.  An  ephemeron  intelligence  could  thus  write  the  his- 
tory of  a  tree  destined  to  endure  a  thousand  years.  It  is 
so  in  the  history  of  a  planet.  Man  is  an  ephemeron  corn- 
pared  with  the  lifetime  of  a  world;  but  while  he  endures, 
he  notes  thousands  of  worlds  in  all  the  different  stages 
of  world-life,  and,  selecting  a  series  of  examples,  he  runs 
them  on  a  continuous  thread,  and  has  a  tale  of  evolu- 
tions which  span  a  million  years.  Individual  histories 
have  begun  at  different  periods  in  the  lapse  of  time;  and. 
individual  histories,  whether  simultaneously  begun  or  not, 
have  been  accelerated  or  retarded  by  differences  in  the 
modifying  conditions. 

Our  earth  has  reached  a  certain  stage  of  development. 
It  happens  at  this  epoch  [to  be  a  habitable  world.  It  is 
supposable  that  its  present  state  has  persisted  from  eter- 
nity; and  this  was  the  belief  of  some  of  the  ancients,  as 
well  as  a  few  of  the  moderns.  Limited  observation,  how- 
ever, shows  that  changes  are  taking  place — that  a  history 
is  in  progress,  and  the  mind  demands  the  past  of  this  his- 
tory—  that  which  lies  back  of  the  observation  of  the 
individual,  or  even  of  the  race.  Now,  availing  ourselves 
of  the  law  of  parallel  history,  we  study  the  phenomena 
of  beach  erosion  and  detrital  accumulation,  and  see  in 
these  a  picture  of  Silurian  times  —  of  geologic  changes 
consummated  thousands  of  years  before  even  our  race  had 
an  existence.  This  is  pure  geology.  But  nothing  in  the 
existing  phases  of  the  planet  can  reveal  the  history  of 
events  which  transformed  the  planet.  Bodily  transfor- 
mations obliterated  all  records  of  what  was  past.  Ge- 
ology has  perpetuated  terrestrial  history  only  by  the  fixed 
forms  of  enduring  rocks.  But  we  find  in  igneous  masses 
intimations  of  an  older  state,  whose  records  were  written 
upon  fluid  matter,  to  be  inevitably  effaced.  Here  is  the 


THE   KEYS   OF   COMPARATIVE   GEOLOGY.  537 

limit  of  possible  geology.  But  we  learn  that  our  earth, 
as  a  whole,  is  but  one  of  a  series  of  planets;  that  these 
planets,  from  their  common  physical  relations,  must  have 
had  a  common  history;  that  before  they  were  planets, 
they  belonged  to  a  category  of  existence  of  which  the 
sun  is  a  type  and  a  remnant;  that,  probably,  in  some 
remoter  epoch  in  the  past  eternity,  all  the  suns  belonged 
to  a  category  of  existence  now  exemplified  in  irresolvable 
nebulfe;  and  we  learn  that  all  these  conditions  are  phases 
in  the  consummated  history  of  our  world  —  that  the 
investigation  of  them  is  at  the  same  time  cosmogony  and 


The  fundamental  data  of  this  comparative  science  of 
world  growth  have  been  already  passed  under  review.* 
The  first  group  of  data  unites  the  earth,  the  planets  and 
the  satellites  in  a  single  category  of  existence.  The  com- 
munity of  movements,  forms  and  conditions  is  such  that 
we  feel  borne  to  the  conclusion  that  whatever  may  be  de- 
termined as  to  the  past  or  future  conditions  of  our  world 
must  be  also  conditions  in  the  life  history  of  each  of  the 
other  planets.  These  relations  have  arrested  the  atten- 
tion of  all  students  of  nature,  and  have  produced  in  the 
most  thoughtful  minds  an  irresistible  conviction  that  the 
members  of  the  Solar  System  constitute  but  one  family 
—  that  all  the  planets  and  satellites  must  have  had  a  com- 
mon starting  point.  This  conviction  has  found  expres- 
sion in  the  theories  propounded  by  Kepler,  Newton, 
Leibnitz,  Kant,  Herschel  and  Laplace. 

The  most  recent  results  of  speculation  concerning  the 
progress  of  cosmical  evolution  I  have  set  forth  in  preced- 
ing chapters.  It  will  be  of  interest  now,  to  glance  from 
our  elevated  standpoint  over  the  whole  realm  of  cosmical 
existence  and  note  synoptically  the  stages  attained  by  the 
different  orders  of  worlds  in  human  times,  and  then  to 

*  Part  II,  chapters  i-iv. 


538  THE    COSMIC    CYCLE. 

follow  the  current  of  events  onward  from  our  present  ter- 
restrial condition  toward  some  far-off  cosmical  finality.* 

g  2.  THE  FINAL  GENERALIZATION. 

Alles  was  endlich  1st,  was  einen  An  fang  nnd  Ursprung  hat,  hat  das  Merkmal 
einer  eingeschrankten  Natur;  es  muss  vergehen  und  ein  Ende  haben.— KANT. 

1.  Stages  of  World-life.  —  The  deepest  principle  of 
change  in  cosmic  existence  is  expressed  by  the  word  cool- 
ing. The  broadest  physical  generalization  to  be  drawn 
from  the  phenomena  of  the  cosmical  realm  is  the  affirma- 
tion of  progressive  reduction  of  temperature.  The  his- 
tory of  a  world  is  a  history  of  cooling.  All  other  world- 
making  activities  come  into  play  concomitantly.  If  the 
process  of  cooling  transforms  also  a  vast  amount  of  me- 
chanical energy  into  the  form  of  heat,  it  is  always,  and 
necessarily,  less  in  amount  than  the  energy  lost  in  trans- 
forming it. 

The  three  great  cosmic  forces  are  heat  and  atomic  and 
molar  attractions.  To  these  should  probably  be  added 
repulsions. 

A  world's  lifetime,  with  its  incidents  and  consequents 
is  but  a  progressive  cooling.  Every  individual  world  in 
the  established  order  of  events,  passes  or  may  pass,  suc- 
cessively through  all  the  stages  and  phases  known  to 
cosmogony.  Cosmic  lifetimes  have  begun  at  different 
epochs,  and  proceed  at  different  rates  of  change.  Some 

*The  present  writer's  first  published  attempt  to  generalize  the  whole  course 
of  cosmical  history  was  a  brochure  entitled  The  Geology  of  the  Stars,  32  pp., 
12mo,  Boston,  1872,  being  No.  7  of  "  Half  Hour  Recreations  in  Popular  Science," 
pp.  255-286.  Almost  simultaneously  appeared  Mr.  Stanislas  Meunier:  Le  Cielgeo- 
logique,  prodrome  de  Gi-ologle  Comparte,  Paris,  1871.  A  descriptive  treatment  of 
the  early  and  remote  future  history  of  our  world,  with  glimpses  of  the  compara- 
tive geology  of  our  system  was  presented  by  the  writer  in  Sketches  of  Creation, 
ISmo,  pp.  459,  with  illustrations,  New  York,  1870.  He  has  also  discussed  the 
subject  in  The  Unity  of  the  Physical  World,  Part  I,  Facts  of  Coexistence, 
Part  II,  Facts  of  Succession,  Meth.  Quarterly  Review,  April,  1873,  and  Janu- 
ary, 1874. 


THE   FIXAL    GENEEALIZATION".  539 

began  so  far  back  in  eternity  or  have  proceeded  at  so 
rapid  a  rate,  that  their  careers  are  brought  to  a  conclu- 
sion in  the  passing  age.  Some  are  even  now  awaking  into 
existence  ;  and  it  is  probable  that  worlds  are  beginning 
and  ending  continually.  Hence  cosmic  existence,  like  the 
kingdoms  of  organic  life,  presents  a  simultaneous  pano- 
rama of  a  completed  cycle  of  being.  A  taxonomic 
arrangement  of  the  various  grades  of  animal  existence 
presents  a  succession  of  forms  which  we  find  repeated  in 
the  embryonic  history  of  a  single  individual,  and  again 
in  the  succession  of  geological  types  ;  so  the  taxonomy 
of  the  heavens  is  both  a  cosmic  embryology  and  a  cosmic 
palaeontology. 

In  endeavoring  to  present  by  way  of  resume,  a  syste- 
matic or  developmental  arrangement  of  cosmical  condi- 
tions, our  thoughts  fix  at  once  npon  four  general  stages 
of  world-life.  These  are  first,  the  Chaotic  or  Prenebular  ; 
second,  the  Nebular  Stage  ;  third,  the  Solar  Stage  ;  and 
fourth,  the  Planetary  Stage.  Under  the  last  three  we  may 
readily  discriminate  several  phases  of  progress.  It  prob- 
ably is  not  possible,  in  the  present  state  of  human  knowl- 
edge, to  arrange  these  phases  in  a  final  consecutive  order. 
Probably  some  phases  are  parallel  with  others,  instead  of 
consecutive.  Nevertheless,  a  developmental  arrangement 
is  a  desideratum  ;  and  the  inexpert  reader  will  be  thank- 
ful for  a  systematic  exhibit  of  the  best  results  science  has 
as  yet  attained,  or  even  for  the  following  resum6  of  the 
discussions  and  conjectures  ventured  upon  in  the  present 
work. 

I.     CHAOTIC    STAGE. 

Cosmical  dust.  Cosmical  atoms  promiscuously  dis- 
persed in  space  ;  gathering  themselves  in  groups  large 
and  small  ;  forming  meteors,  meteoroidal  trains  and  prob- 
ably comets;  in  their  larger  aggregations  becoming 
nebular  dust,  either  cold  or  partially  heated. 


540  THE   COSMIC    CYCLE. 

II.    NEBULAR    STAGE. 

1.  Normal  Nebular  Phase. — Faintly  luminous  matter 
consisting  perhaps  of  mineral  mist  formed  of  incandes- 
cent liquid  or  solid  particles  floating  in  a  luminous,  gas- 
eous medium,  or  of  stony  particles  and  masses  whose 
mutual  collisions  develop  heat  and  incandescent  gases. 
Spectrum  consisting  of  one,  two,  three  or  four  bright 
lines,  or  perhaps  of  five  or  more,  revealing  the  presence  of 
nitrogen  and  hydrogen,  and  sometimes  superposed  on  a 
faint  continuous  spectrum.  Density  low  and  heat  less 
than  that  of  our  sun.  Exemplified  in  certain  irresolvable 
nebulae. 

NOTE. — The  thermal  incandescence  of  the  normal  nebula  remains 
to  be  fully  established. 

2.  Nebular  Fire  Mist. — Mineral  mist  increased  in  quan- 
tity, but  a  gaseous  medium  still  predominant.     Condensa- 
tion and  evolution  of   heat   in    progress.        Spectrum  of 
bright  lines  superposed  on  a  faint  continuous  spectrum, 
showing  presence  of  fire  mist. 

A.  Continuous  fire  mist.     The  nebular  mass  remains  homogen- 
eous and  its  luminous  constituents  mostly  gaseous.     Certain 
irresolvable  nebulae,  as  H.  4,374.     Also  a  small  number  of 
stars,  as  Gamma  of  Cassiopoaia  and  Beta  of  the  Lyre. 

Annulations  perhaps  begin  in  this  phase.  The  primitive 
nebula  may  thus  be  resolved  into  solar  nebulae  in  which  other 
annulations  succeed;  or  if  the  mass  is  insufficient,  it  may 
proceed  with  only  the  evolutions  of  a  solar  nebula.  Annular, 
and  probably  spiral  and  falcate  nebulae  belong  here,  the  two 
latter  illustrating  a  disturbed  state  of  anntilation.  Satur- 
nian  rings  persisting  like  a  preserved  embryo,  exemplifying 
the  form  but  not  the  stage. 

B.  Discontinuous  fire  mist.     Phase  parallel  with  A.     Nebula  un- 
dergoing segregation  and  accumulation  around  local  nuclei 
without  annulation.     Also,  entire  nebulae  slowly  condensing 
around  single  nuclei.      Certain  resolvable  nebula?  (compare 
nebula  in  Draco). 

3.  Nucleating  Phase. —  Distinct   central  condensation. 


THE   FLNAL   GENERALIZATION.  541 

Photospheric  matter  increased,  but  the  gaseous  medium 
predominant.  Bright  lines  over  a  continuous  spectrum. 
Sun  systems  and  planetary  segregations  past  the  stage  of 
annulation.  Planetary  nebulae,  especially  H.  838,  H.  464, 
H.  2,098  and  H.  2,241.*  Also  Nebulous  Stars,  as  H.  450. 

4.  Nucleated  Phase. —  Condensation  more  advanced. 
Temperature  and  luminosity  of  the  fire  mist  so  increased 
that  the  absorbent  power  of  the  gaseous  atmosphere  is 
precisely  neutralized  and  the  spectrum  is  continuous. 
Point  of  transition  from  bright-line  spectra  to  dark-line 
spectra.  Phase  observed  probably,  in  certain  star  clusters, 
and  most  resolvable  nubulce. 

XOTE. — The  continuous  spectrum  may,  in  some  cases,  be  only 
apparent,  the  fineness  of  the  lines  rendering  them  invisible  with  exist- 
ing instruments. 

III.     STELLAR    STAGE. 

1.  Sirian    Phase. —  Increased   condensation   and    in- 
creased heat.     Atmosphere  increased  in  volume  and  ten- 
sion.    Absorbent    capacity  exceeds  the  emissive.     Spec- 
trum continuous  and  crossed  by  four  dark  lines  having  an 
extraordinary  breadth.    White  Stars  (Secchi's  First  Type). 

XOTE. — The  mass  of  the  star,  independently  of  its  age,  would  in- 
fluence the  tension  of  the  absorbent  medium,  and  hence  the  width  of 
the  dark  lines.  We  cannot  be  certain,  therefore,  from  spectroscopic 
indications,  that  this  phase  precedes  the  next.  Guided  by  color 
alone,  the  white  stars  should  precede  the  yellow. 

2.  Capellar  Phase, — Absorbent  atmosphere    reduced 
in  depth  and  consequent  tension,  to  such  an  extent  as  to 
give   very    numerous    dark    absorption    lines    of    normal 
breadth.     Spectrum  identical  with  normal  spectrum  of  the 
sun.      Yellow  Stars  (Secchi's  Second  Type). 

Some  fixed  stars  in  the  last  two  phases,  the  centres  of 
cosmic  systems.  Some  have  attendant  worlds  still  lumi- 
nous. Sirius  is  a  sun  with  four  still  luminous  planets. 

*  These  designations  refer  to  Herschel's  Catalogue  of  Nebulae. 


542  THE    COSMIC    CYCLE. 

Procyon,  Rigel,  Aldebaran,  Arcturus,  Antares,  £  Can- 
cri,  etc.,  have  each  one  or  more.  Some  of  these  com- 
panions have  still  smaller  attendants,  as  fi  Lupi,  ij  Lyrce, 
s  Cancri,  12  Lyncis,  0  Orionis.  These  are  still  luminous 
satellites. 

3.  Solar  Phase. —  Photospheric  matter  copious.     At- 
mosphere in  a  high  state  of  activity,  and  still  causing  a 
spectrum  of  dark    lines.       The   heated   nucleus    ejecting 
gases  through  the  photosphere,  which  fall  back,  on  cooling, 
and  form  dark  spots  on  the  surface  of  the  photosphere. 
Incipient  variability. 

A.  Phase    of    the    gaseous    nucleus    continually    diminishing. 
Probably  our  own  sun. 

B.  Phase  of  the  molten  nucleus  continually  increasing.    This 
succeeding  phase  A. 

4.  Variable  Phase. —  Photosphere  periodically  dark- 
ened  by  the  condensation  of  large   amounts  of  macular 
matter.     Probably  approaching  total  liquefaction.     Spec- 
trum as   in  Second   Phase,  but  with  numerous  nebulous 
bands  brightest  on  the  side  toward  the  red.    Periodic  and 
Irregular    Stars  (Secchi's    Third  Type).     Some  variable 
stars  probably  advanced  to  incipient  incrustation. 

5.  Molten  Phase. — Photospheric  matter  exhausted  by 
precipitation.     Absorbent  media  greatlv  reduced.     A  mol- 
ten globe.     Spectrum  continuous.     Probably  some  of  the 
Star  Clusters  and  Resolvable  Nebula?. 

6.  Incrustive  Phase. —  Early  periods  of    incrustation. 
The  light  becomes  ruddy.    Incipient  darkening.    Spectrum 
of  dark  linos,  but  crossed  bv  three  bright  bands,  brightest 
on  the  side  toward  the  violet.    Red  Stars  (Secchi's  Fourth 
Type). 

NOTE. — I  am  much  in  doubt  concerning  the  proper  position  of 
the  "red  stars."  Their  spectra,  unless  some  explanation  can  he 
given,  would  place  them  between  the  Nebular  and  Stellar  Stages.  I 
assume,  therefore,  that  the  early  incrustive  phase  is  one  which  pre- 
sents the  reproduction  or  fresh  disengagement,  of  some  enveloping 


THE    FINAL   GENERALIZATION".  543 

absorbent  medium.  I  have  already  recorded  my  conviction  that  it 
is  a  phase  of  aqueous  condensation  and  aqueous  gaseity  —  the  pre- 
lude of  the  stormy  period. 

7.  Eruptive  Phase. — Crust  so  darkened  as  to  be  invisi- 
ble as  a  star;  but  disrupted  at  intervals,  giving-  spasmodic 
luminosity,  which  shines  through  an  atmosphere  of  aque- 
ous vapor  and  gas.  Spectrum  continuous,  and  crossed  by 
dark  lines  like  the  solar  spectrum,  with  a  superposed 
spectrum  of  four  bright  lines.  Temporary  Stars,  also  f 
Cassiopoeice,  ft  Lyrce  (variable)  and  r,  Argus  (Secchi's  Fifth 
Type). 

NOTE. — The  phenomena  of  a  temporary  star  may  recur  many 
times  during  the  progress  of  the  planetary  phases,  and  thus  give  the 
star  a  remotely  periodic  character.* 

IV.     PLANETARY  STAGE. 

1.  Jovian  Phase, — The   incrustive    phase   has  passed 
into  the  stormy  phase.     A  water  mist  condenses  in   the 
peripheral  regions,  as  formerly  the  fire  mist  appeared.     It 
gathers  into  a  vaporous  envelope  constituting  a  true  atmos- 
phere  or   nephelosphere.      This    precipitates    an   aqueous 
rain,  the  homologue  of  the  molten  rain  of  earlier  times. 

A.  Phase  of  fading  luminosity.     Crust  not  yet  darkened  or  cool 
enough  to  receive  the  rains.     Phase  of  Jupiter. 

B.  Phase  of  the  primeval  ocean.     Protophytic  and  later,  proto- 
zoic  life,  on  planets  otherwise  suitably  conditioned. 

2.  Terrestrial  Phase. — Aqueous  precipitation  periodi- 
cal.    Cyclonic  movements  of  the  atmosphere,  perhaps  the 

*  The  writer  is  fully  aware  of  the  insufficiency  of  the  known  data  for  corre- 
lating the  various  phases  of  cosmical  matter,  and  of  the  rashness  of  his  own 
attempt  to  do  what  has  not  been  attempted  by  the  masters  of  stellar  physics. 
We  need  to  know  much  more  yet  respecting  the  relations  of  spectra  to  tempera- 
ture, pressure  and  molecular  arrangement;  and  also,  in  view  of  the  analogies 
drawn  from  light  in  Geislerian  tubes,  more  of  the  connection  between  the  ten- 
sion of  the  electric  current  and  the  temperature  and  density  of  the  gas  made 
luminous  by  the  electric  discharge.  The  reader,  nevertheless,  who  will  avoid 
placing  too  much  stress  upon  the  details  of  the  foregoing  arrangement,  will  ob- 
tain a  correct  impression  of  the  great  fact  of  progressive  changes  in  cosmical 
matter. 


544  THE   COSMIC    CYCLE. 

homologues  of  those  which  cause  solar  maculations.  Period 
of  organic  life,  embracing  its  culmination.  The  Earth, 
and  possibly  Venus  and  some  of  the  satellites  of  Jupiter. 

3.  Martial    Phase. — Planetary    senescence.       Dimin- 
ished  vapors    and    infrequent    rains.      Encroaching   cold. 
Decline  of  organic  development.     Mars,  and  possibly  the 
Jovian  satellites. 

4.  Synchronistic  Phase. — Tidal  retardation  of   rotary 
motion  progressing,  and  reaching  its  finality.     Moon,  and 
probably  all  the  older  satellites. 

NOTE. — This  is  not  a  true  consecutive  phase  connected  with  the 
progress  of  inherent  or  developmental  change,  but  a  state  growing 
out  of  relations  to  other  bodies.  It  may  be  reached  sooner  or  later, 
according  to  the  efficiency  of  the  tidal  action  exerted. 

5.  Lunar  Phase. —  Planetary  death.      Disappearance 
of  aqueous  vapors  and  total  absorption  of  water  and  at- 
mosphere.    Extinction  of   organization.      Final  refrigera- 
tion, exemplified  in  the  Moon.     In  bodies  with  an  excess 
of  water  and  air,  the  surface  becomes  ice-covered  and  the 
copious   atmosphere    remains   laden   with    frozen    vapors. 
Saturn,  Uranus  and  Neptune  and  their  satellites. 

However  conjectural  some  parts  of  the  foregoing  ar- 
rangement may  be,  there  is  little  doubt  that  its  general 
tenor  expresses  a  fact  in  the  aspects  of  the  universe.  This 
I  have  endeavored  to  explain  and  impress.  We  know 
enough  of  the  phases  of  matter  in  the  different  provinces 
of  space  to  feel  certain  that  they  represent  progressive 
stages  in  the  natural  evolution  of  matter  as  such.  Whether 
seen  in  nebula,  star,  sun,  planet  or  satellite,  it  is  a  phase 
in  a  common  history,  the  earliest  periods  of  which  are  as 
truly  a  part  of  the  history  of  our  world  as  the  achieve- 
ments of  Alfred  the  Great  are  a  part  of  the  history  of 
communities  of  American  birth. 

6.  Some   Final  Deductions. — These   views  are   calcu- 
lated to  produce  upon  our  minds  a  profound  irnpression  of 


THE   FINAL   GENERALIZATION.  545 

the  unity  of  the  universe,  both  in  its  spatial  extent  and  its 
historical  development.  When  we  combine  with  these 
evidences  the  indications  of  the  presence  of  a  common 
ether  or  other  luminiferous  medium,  and  of  the  supremacy, 
everywhere,  of  the  universal  law  of  gravitation,  we  are 
placed  in  possession  of  an  overwhelming  demonstration  of 
the  identity  of  the  government  which  controls  natural 
events  upon  our  planetary  abode,  and  in  departments  of 
space  so  remote  that  light  occupies  hundreds  of  years  in 
traversing  the  distance.  Whatever  intelligence,  power  or 
goodness  may  seem  to  be  exemplified  in  the  ordinations  of 
terrestrial  affairs,  is  not  less  certainly  illustrated  in  the 
phenomena  which  we  trace  to  the  utmost  verge  of  the 
visible  universe,  and  to  the  remotest  conceivable  com- 
mencement of  material  history.  The  intelligent  Power 
whose  supreme  control  is  recognized  within  the  narrow 
limits  of  personal  experience  is  ONE  through  stretches  of 
space  and  time  which,  to  human  faculties,  are  infinite. 

The  study  of  stellar  geology  leaves  us  with  another 
reflection.  Every  phase  of  matter  seen  in  the  universe  is 
a  transient  one.  The  various  phases  sustain  demonstrably 
some  sort  of  historical  relation  to  each  other.  These 
states  of  matter  are  progressive.  We  trace  them  back- 
ward toward  earlier  conditions  —  toward  an  earliest  con- 
dition, beyond  which  we  know  no  possibility  of  cosmical 
existence.  From  that  condition  to  the  present  is  but  a 
finite  career,  however  vast  the  interval  appears  expressed 
in  numbers.  The  history  began  in  time;  it  does  not  come 
down  to  us  from  eternity.  The  material  organism  is, 
therefore,  originated  in  time.  Now,  when  we  carry  our 
thoughts  back  to  that  primal  condition  indicated,  we  must 
necessarily  perceive  that  it  existed  absolutely  unchanged 
and  unprogressive  from  all  eternity,  or  the  matter  itself 
which  exemplifies  it  did  not  exist  from  eternity.  But  we 
have  not  the  slightest  scientific  ground  for  assuming  that 


546  THE   COSMIC    CYCLE. 

matter  existed  in  a  certain  condition  from  all  eternity, 
and  only  began  undergoing  its  changes  a  few  millions  or 
billions  of  years  ago.  The  essential  activity  of  the  pow- 
ers ascribed  to  it  forbids  the  thought.  For  all  that  we 
know  —  and,  indeed,  as  the  conclusion  from  all  that  we 
know  —  primal  matter  began  its  progressive  changes  on 
the  morning  of  its  existence.  As,  therefore,  the  series  of 
changes  is  demonstrably  finite,  the  lifetime  of  matter  itself 
is  necessarily  finite.  There  is  no  real  refuge  from  this 
conclusion;  for,  if  we  suppose  the  beginning  of  the  pres- 
ent cycle  to  have  been  only  a  restitution  of  an  older  order 
effected  by  the  operations  of  natural  causes,  and  suppose 
—  what  science  is  unable  to  comprehend  —  that  older 
order  to  be  a  similar  reinauguration,  and  so  on  indefinitely 
through  the  past,  we  only  postpone  the  predication  of  an 
absolute  beginning,  since,  by  all  the  admissions  of  modern 
scientific  philosophy,  it  is  a  necessity  of  nature  to  run 
down.  No  former  condition  is  completely  reproduced. 
The  total  energy  in  the  cosmic  organism  diminishes.  A 
finality  is  impending,  and  hence  a  past  eternity  would 
have  sufficed  to  reach  it  an  eternity  since,  and  we  should 
not  be  witnesses  of  the  continued  progress  of  events. 
Whatever  process  from  an  infinite  beginning  involved  an 
end  is  now  a  process  ended,  not  continuing.  The  conclu- 
sion is  unavoidable  that  the  cosmic  organism  began  in 
time,  and  that  the  very  existence  of  matter  is  limited  in 
the  past. 

The  dependent  existence  and  finite  origin  of  matter 
are  revealed  in  its  ultimate  constitution.  The  scenes 
which  we  have  been  contemplating  are  characterized  by 
ceaseless  nutation  and  transformation.  The  very  notion 
of  an  evolution  presupposes  this.  The  progressive  activ- 
ity of  nature's  forces  continually  rebuilds  the  material 
organism.  The  old  disintegrates  and  reappears  trans- 
formed. Nothing  is  permanent.  The  ponderous  forms  of 


THE   FINAL  GENERALIZATION.  547 

worlds  come  and  go.  Suns  are  kindled  and  extinguished. 
Constellations  spread  the  floor  of  heaven  for  a  time,  to  be 
swept  away  by  the  aeonic  march  of  events.  In  the  pro- 
gress of  eternity  how  many  cycles  of  world-life  have  been 
spent;  what  vicissitudes  has  each  molecule  of  matter 
experienced;  how  many  stations  has  it  occupied,  how 
many  functions  performed.  But  we  pause.  This  very 
witness  of  cosmic  changes  testifies  to  something  perma- 
nent and  changeless.  The  molecule  has  not  changed. 
As  hydrogen,  as  silipa,  as  water,  or  other  form  of  matter, 
it  maintains  its  identity  in  all  the  worlds,  in  all  the  re- 
motest spaces  of  the  realm  of  cosmic  existence.  It  throbs 
in  Sirius  with  the  same  signal  as  in  Capella.  Its  vibra- 
tions are  measured  by  the  same  infinitesimal  in  Orion  and 
in  the  sun,  and  in  the  laboratory  of  the  experimenter. 
The  quartz  molecule  which  forms  the  gravel  of  the  garden 
walk  is  the  same  which  slept  for  ages  in  the  masses  of  Ar- 
chaean quartzite.  When  the  quartzite  came  into  existence, 
the  molecule  was  ancient.  It  had  taken  part  in  the  history 
of  the  molten  ages  of  the  planet;  it  had  been  part  of  the 
primordial  fire  mist  in  which  the  first  lines  of  cosmic 
organization  were  traced.  It  grows  into  nothing  else;  it 
grew  out  of  nothing  else;  it  is  primordial,  completed  and 
perfect.  It  was  not,  like  everything  else,  compounded;  it 
was  not  evolved;  it  does  not  disintegrate  or  become  effete. 
The  mutations  which  we  have  traced  belong  to  the  forms 
of  matter.  The  molecule  belongs  to  a  different  category 
of  existence.  If  we  conceive  the  molecule  resolvable  into 
atoms,  then  the  conclusion  remains  of  the  atoms.  Be- 
tween the  changeful  and  the  changeless  is  an  infinite 
gulf.  And  with  all  their  qualities  of  permanence  and 
indestructibility  and  perfection  and  uniformity,  the  mole- 
cule has  been  multiplied  by  millions  of  millions  of  mil- 
lions—  each  molecule  cast  in  the  same  mould,  endued 
with  the  same  form,  animated  by  the  same  energies. 


548  THE  COSMIC   CYCLE. 

How  has  it  been  multiplied?  In  a  universe  organized 
through  processes  of  evolution,  what  is  the  origin  of  a 
thing  unevolved?  In  a  world  of  effects  and  causes,  what 
is  the  cause  of  a  thing  which  had  no  antecedent  ?  Our 
thought  here  trembles  on  the  primal  verge  of  being. 
Beyond — is  the  abyss  of  nothingness;  here  —  are  the 
seeds  of  a  universe.  These  are  not  grown  in  the  nursery 
of  the  natural  world. 

Finally,  as  just  intimated,  the  future  life  of  cosmical 
organization  is  as  clearly  set  within  limits  as  its  past. 
There  is  an  ultimate  goal  toward  which  all  cosmical 
matter  is  tending.  That  goal  is  not  the  actual  condition 
of  our  world,  for  we  see  here  everything  in  a  state  of 
change;  and  the  moon  exemplifies  an  ulterior  state.  It 
cannot  be  the  Lunar  phase,  for  even  there  solar  light  and 
heat,  and  terrestrial  influences,  and  universal  gravitation, 
and  meteoric  matter,  and  a  pervading  ether,  are  all  con- 
spiring to  disturb  the  condition  of  absolute  repose.  The 
finality  lies  in  the  impenetrable  darkness  of  the  distant 
future.  What  it  may  be  we  can  only  conjecture;  but  one 
impending  stage  of  all  cosmical  matter  is  positively  writ- 
ten upon  the  face  of  the  moon.  Not  only  must  our  own 
planet  reach  finally  that  refrigerated  and  inhospitable  con- 
dition, but  the  sun  itself  must  ultimately  fade  to  a  dark- 
ened planet  and  become  extinguished  in  the  heavens. 

These  thoughts  summon  into  our  immediate  presence 
the  measureless  past  and  the  measureless  future  of  mate- 
rial history.  They  seem  almost  to  open  vistas  through 
infinitv,  and  to  endow  the  human  intellect  with  an  exist- 
ence and  a  vision  exempt  from  the  limitations  of  time  and 
space  and  finite  causation,  and  lift  it  up  toward  a  sublime 
apprehension  of  the  Supreme  Intelligence  whose  dwelling 
place  is  eternity. 


PART  IT. 

EVOLUTION   OF  COSMOGO^rIC 
DOCTRINE. 


Les  Savants  sont  de  nos  jours  unanimes  a  admettre  que  notre  systerae 
solaire  est  du  a  la  condensation  d'une  nebuleuse  qui  etendait  autrefois  au-dela 
des  limites  occupies  actuellement  par  les  planetes  le  plus  lointaines  *  *  * 
La  the"orie  *  *  *  a  £te  bien  confirm^,  et,  pour  ainsi  dire,  demontre  par  la 
de'couverte  des  n^buleuses  gazeuses. —  Le  Pere  SECCHI. 


PART  IV. 
EVOLUTION  OF   COSMOGONIC  DOCTRINE. 

WHEN  a  great  theory  has  grown  into  existence,  and 
the  general  assent  of  competent  judges  has  con- 
verted a  sublime  conception  from  the  state  of  a  provi- 
sional hypothesis  to  the  position  of  a  strengthening  doc- 
trine, there  is  unusual  interest  in  glancing  over  the  pro- 
gress of  science  and  noting  the  actual  steps  by  which  the 
guess  became  theory,  and  the  theory,  doctrine.  I  shall 
therefore  supplement  the  subject  of  nebular  cosmogony 
with  a  concise  historical  sketch.  This  I  think  will  be  ac- 
ceptable to  the  reader  because  cosmological  science  has 
now  attained  such  a  position  that  every  intelligent  person 
should  possess  some  information  respecting  the  exact 
views  of  Kant,  Herschel  and  Laplace,  the  chief  founders 
of  this  science  as  now  accepted  ;  while  no  adequate  sum- 
mary of  their  speculations  —  most  especially  those  of 
Kant  —  is  sufficiently  accessible  to  the  general  reader. 


CHAPTER  I. 

PRE-KANTIAN    SPECULATIONS. 
§  1.  GREEK  PHILOSOPHERS. 

THE  familiar  phenomena  of  whirlwinds,  whirlpools 
and  eddies  seem  to  have  suggested  to  reflecting 
minds  in  all  ages,  the  possibility  of  some  vortical  theory 
for  the  explanation  of  the  mechanism  of  the  world.  The 
diurnal  and  annual  motions  of  the  heavenly  bodies  were 
early  submitted  to  an  attempt  at  solution  based  succes- 
sively upon  Eudoxian,  Hipparchian  and  Ptolemaic  systems 
of  cycles  and  epicycles.  When  the  Copernican  theory 
began  to  gain  a  foothold,  it  could  no  longer  be  doubted 
that  the  method  of  vortices  was  the  method  of  the  heav- 
ens. We  now  understand  how  the  mutual  actions  of  the 
numerous  bodies  in  the  material  universe  must  result  in  a 
general  and  most  intricate  network  of  virtual  revolutions 
about  centres  of  gravity. 

The  doctrine  of  the  rotation  of  the  earth  about  an  axis 
was  taught  by  the  Pythagorean  Hicetas,  probably  as 
early  as  500  B.C.  It  was  also  taught  by  his  pupil  Ec- 
phantus,  and  by  Heraclides,  a  pupil  of  Plato.  The  im- 
mobility of  the  sun  and  the  orbital  rotation  of  the  earth 
were  shown  by  Aristarchus  of  Samos  as  early  as  281  B.C., 
to  be  suppositions  accordant  with  facts  of  observation. 
The  heliocentric  theory  was  also  taught,  about  150  B.C., 
by  Seleucus  of  Seleucia  on  the  Tigris.*  It  is  said  also 
that  Archimedes,  in  a  work  entitled  Psammites,  incul- 

*  Compare  Whewell:  History  of  the  Inductive  Sciences,  Am.  ed.  i,  259; 
Delambre :  Astronomte  Ancienne. 

551 


552  PRE-KANTIAN    SPECULATIONS. 

cated  the  heliocentric  theory.  The  sphericity  of  the 
earth  was  distinctly  taught  by  Aristotle,  who  appealed 
for  proof  to  the  figure  of  the  earth's  shadow  on  the  moon 
in  eclipses.*  The  same  idea  was  defended  by  Pliny,  f 
These  views  seem  to  have  been  lost  from  knowledge  for 
more  than  a  thousand  years.  In  1356,  Sir  John  Maunde- 
ville  in  his  remarkable  book  of  travels  distinctly  and  in- 
telligently revived  the  ancient  idea.  J  In  1346,  Nicolaus 
Ousanus  wrote  a  work  §  in  which  the  idea  of  the  Greeks 
was  scientifically  defended.  Thus  was  opened  the  way 
for  Copernicus.|| 

The  introduction  of  the  vortical  conception  into  theo- 
ries of  the  origin  of  things  dates  from  an  antiquity  equally 
high.  According  to  Anaxagoras  of  Clazomenae,  who  was 
born  about  500  B.C.,  the  primitive  condition  of  things 
was  a  heterogeneous  commixture  of  substances  which 
continued  motionless  and  unorganized  for  an  indefinite 
period.  "  Then  the  Mind  began  to  work  upon  it,  commu- 
nicating to  it  motion  and  order. ^j  The  Mind  first  effected 
a  revolving  motion  at  a  single  point  ;  but  ever-increasing 
masses  were  gradually  brought  within  the  sphere  of  this 
motion,  which  is  still  incessantly  extending  farther  and 
farther  in  the  infinite  realm  of  matter.  As  the  first  conse- 
quence of  this  revolving  motion,  the  elementary  contra- 
ries, fire  and  air,  water  and  earth,  were  separated  from 
each  other.  But  a  complete  separation  of  dissimilar, 
and  union  of  similar  elements  was  far  from  being  hereby 
attained,  and  it  was  necessary  that  within  each  of  the 

*  Aristotle:  De  Cirlo,  lib.  ii.  cap.  xiv. 

t Pliny:  Natural  History,  ii,  65. 

%  The  Volage  and  Travaile  of  Sir  John  Maundeville,  Kt.,  from  the  ed.  of 
1725.  London,  1866.  Chap,  xvii,  especially  pp.  180-182. 

§  De  Docta  Ignorantia. 

Aryabatta,  an  Indian  astronomer,  about  1322,  A.D.,  and  some  of  his  coun- 
trymen, are  said,  however,  to  have  taught  the  heliocentric  doctrine.  Draper  : 
Intellectual  Development  of  Europe.  145. 

'Aristotle  :  Phyiica,  viii,  1.    Also,  Diog.  Laertius:  Lives. 


SPECULATIONS   OF   KEPLER.  553 

masses  resulting  from  this  first  act,  the  same  process 
should  be  repeated."  *  The  views  of  Leucippus,  and  of 
Democritus,  his  disciple,  promulgated  about  430  B.C., 
present  a  closer  relation  to  some  aspects  of  the  modern 
nebular  theory.  They  maintained  that  space  was  eter- 
nally filled  with  atoms  actuated  by  an  eternal  motion. 
The  weight  of  the  larger  atoms  forced  them  downward, 
while  simultaneously  the  lighter  ones  were  thrust  upward. 
Mutual  collisions  produced  lateral  movements.  Thus 
rotary  motion  was  generated,  "  which  extending  farther 
and  farther,  occasioned  the  formation  of  worlds."  f  These 
views  were  extended  by  Epicurus  and  the  Roman  Lu- 
cretius, J  though  by  them  the  lateral  motion  of  the  atoms 
was  ascribed  to  choice  —  a  conception  of  the  animated 
nature  of  atoms  which  has  been  revived  again  and  again, 
and  especially  in  the  seventeenth  century  by  Gassendi 
and  Leibnitz,  and  in  the  nineteenth  century  by  Rosmini, 
Campanella,  Bruno  and  Maupertuis. 

§  2.   SPECULATIONS  OP  KEPLER. 

The  celebrated  Kepler,  about  1595,  devised  a  curious 
hypothesis  which  made  use  of  a  vortical  movement  within 
the  solar  system.  The  conception  of  attraction  and  repul- 
sion had  come  down  from  the  epoch  of  Empedocles,  by 
whom  they  were  designated  "love"  and  "hate;"  but  to 
the  time  of  Kepler,  no  interaction  between  masses  of  mat- 
ter had  been  distinctly  recognized  which  was  generically 
different  from  magnetism.  When,  therefore,  Kepler  pro- 
jected a  theory  employing  attraction  and  repulsion,  he 
attributed  these  actions  to  cosmical  magnetism.  The  sun 
was  regarded  by  him  as  a  great  magnet  revolving  on  an 

*  Ueberweg:  History  of  Philosophy,  i,  66. 

t  These  views  seem  to  have  been  quite  definitely  formulated  by  Leucippus, 

though  they  are  generally  attributed  to  Democritus.  See  Diogenes  Laertius :  Lives. 

i  Similar  theories  were  long  afterward  entertained  by  Torricelli  and  Galileo. 


554  PRE-KANTIAN    SPECULATIONS. 

axis  whose  position  had  been  determined  by  the  Divine 
Being.*  The  solar  substance  was  immaterial,  and  sent 
forth  radially  an  emanation  of  the  same  substance. 
These  radiations  rotated  with  the  sun,  and  thus  consti- 
tuted a  vortex.  The  whole  surface  of  the  sun  was  re- 
garded as  attractive,  while  the  centre  was  repulsive. 
These  two  forces  were  everywhere  in  equilibrium,  and 
hence  a  planet  in  any  appointed  position  would  be  retained 
constantly  at  its  mean  distance,  and  would  be  carried 
around  the  sun  in  its  vortex.  The  departure  of  the  plane- 
tary paths  from  the  circular  form  was  explained  by  the 
supposition  that  each  planet  had  one  attractive  side  and 
one  repulsive  side  and  that  these  were  turned  alternately 
toward  the  sun.  Thus  when  the  attractive  side  was  turned 
toward  the  sun,  the  planet  approached  a  perihelion,  and 
when  the  opposite  side  was  thus  turned,  the  planet  retired 
to  its  aphelion.  The  deviation  of  the  orbital  plane  from 
the  equatorial  plane  of  the  sun  was  accounted  for  by  the 
supposition  that  the  planet  was  furnished  with  certain 
'fibres"  which,  acting  like  a  rudder  against  the  sea  of 
solar  emanations,  guided  the  body  above  or  below  the 
plane  of  the  solar  equator.  Kepler,  perceiving  that  the 
motion  of  the  central  sun  must  in  time  be  diminished  and 
exhausted,  provided  for  its  constant  restoration  by  the 
perpetual  care  of  the  Creator,  or  by  the  assistance  of  a 
spirit  designated  for  that  employment. 

A  hypothesis  more  fanciful,  and  less  in  accord  with  the 
requirements  of  physical  principles  has  not  been  offered  in 
ancient  or  modern  times. 

§  3.  THE  VORTICAL  THEORY  OF  DESCARTES. 

By  far  the  ablest  expositor  of  a  vortical  conception  of 
the  universe,  without  ostensible  appeal  to  universal  attrac- 

*8ee  Gregory:  Elements  of  Astronomy,  Sec.  10,  Prop.  66;  Delambre:  As- 
tronomie  du  Moyen  Age. 


THE   VORTICAL   THEORY   OF   DESCARTES.  555 

tion,  was  Descartes.*  He  assumed,  in  brief,  that  infinite 
space  is  filled  with  infinite  matter;  that  matter  was  origi- 
nally in  a  chaotic,  formless  condition;  that  the  cosmical 
bodies  arose  at  first  from  vortical  motions  in  the  original 
mass.  These  bodies  float  in  the  rotating  matter  like  a  sleep- 
ing traveller  in  a  ship  at  sea.  Gravitation  was  not  recog- 
nized, and  all  physical  phenomena  were  explained  by  the 
laws  of  pressure  and  impulsion  alone. 

More  particularly,  Descartes  supposed  that  all  matter 
was  in  the  beginning  divided  by  God  into  particles  of 
nearly  equal  size.  They  were  small  and  were  actuated  by 
motions  about  their  own  centres.  Not  being  in  absolute 
contact,  the  universal  substance  was  of  the  nature  of  a 
fluid.  Groups  of  particles  rotated  also,  about  other  cen- 
tres remote  from  each  other  and  thus  established  a  corre- 
sponding number  of  vortices.  Mutual  friction  reduced 
the  particles  to  globules  of  various  sizes,  which  he  desig- 
nates "  particles  of  the  second  element."  The  matter  of  the 
- "  first  element "  consisted  of  minute  parts  rubbed  from 
the  corners  of  the  globules.  This  matter  rotated  with 
great  rapidity.  Its  abundance  was  more  than  sufficient  to 
fill  the  interstices  between  the  globules,  and  the  surplus 
was  collected  at  the  centre  of  the  vortex,  in  consequence 
of  the  retirement  of  the  globules  by  virtue  of  their  circu- 
lar motion.  The  centrally  accumulated  fluid  became  a 
sun  in  the  centre  of  each  vortex.  The  sun  had  a  rapid 
rotation  about  its  axis,  in  common  with  the  motion  of  the 
surrounding  particles,  and  it  also  continually  emitted 
some  of  its  own  substance  which  escaped  radially  with  a 

*  His  views  are  set  forth  comprehensively  in  the  work  entitled  Renati  Des- 
cartes Principia  Philosophic,  Amsterdam,  1644.  Many  editions  of  the  complete 
works  and  of  single  works  of  Descartes  have  been  published  in  Latin,  French 
and  German.  Perhaps  the  best  is  (Euvres  de  Descartes,  nouvelle  edition  pre- 
ct;de  d'une  introduction  par  Jules  Simon,  Paris,  1868.  A  summary  of  Descar- 
tes' vortical  theory  may  he  found  in  David  Gregory's  Elements  of  Astronomy, 
Physical  and  Geometrical,  1701.  See,  also,  in  the  Encyclopedia  Britannica, 
Art.  Descartes. 


556  PRE-KANTIAN    SPECULATIONS. 

spiral  motion,  through  the  narrow  passages  between  the 
globules  along  the  plane  of  the  equator.  These  emana- 
tions, in  their  vortical  movement  carried  the  globules  with 
them.  But  those  nearest  the  centre  moved  with  a  higher 
velocity  than  those  more  remote,  and  must  therefore  have 
been  smaller;  for  if  of  equal  or  greater  mass,  their  greater 
momentum  would  have  carried  them  off  to  the  greater  dis- 
tances instead  of  the  less.  What  is  affirmed  of  any  one 
vortex  may  be  similarly  affirmed  of  every  vortex.  But 
beyond  a  certain  limit  of  distance  from  the  centre,  the 
globules  are  assumed  to  revolve  with  a  quicker  motion  and 
to  be  of  sizes  as  small  as  the  lower  ones.  The  orbit  of 
Saturn  marks  this  limit  in  the  solar  vortex. 

Descartes  posited  also  a  "third  matter,"  produced  from 
the  original  particles.  As  the  "first  matter,"  resulting 
from  friction,  settles  through  the  interstices  between  the 
rapidly  revolving  globules  it  becomes  "twisted  and  chan- 
nelled," and  when  it  reaches  the  central  orb  it  rests  upon 
its  surface  like  froth  or  foam,  and  constitutes  spots,  like 
those  seen  on  the  surface  of  the  sun.  In  some  cases,  this 
foam  dissolves  into  an  ether  surrounding  the  sun;  but  in 
others  it  accumulates  in  a  thick  and  dense  crust  which 
weakens  the  expansive  force  of  the  central  body. 

Now,  if  we  suppose  the  central  sun  of  any  vortex  to 
become  so  "covered  with  spots"  as  to  be  materially 
"weakened"  it  would  be  gradually  overcome  by  the  vorti- 
cal whirl  of  a  neighboring  sun.  If  now,  this  subjugated 
sun  possess  a  feebler  power  of  agitation,  or  have  less 
solidity  than  the  globules  of  the  second  element  moving 
near  the  circumference  of  the  subjugating  vortex,  but 
more  than  those  nearer  the  centre  of  the  vortex,  then  the 
subjugated  sun  will  descend  through  the  sujugating  vortex 
until  it  arrives  at  a  point  where  its  solidity  or  aptitude  to 
persevere  in  motion  along  a  straight  line,  is  equalled  by 
that  of  the  globules  there  surrounding  it.  In  this  situa- 


THE   VORTICAL   THEORY    OF    DESCARTES.  557 

tion  it  will  float  in  equilibrium  in  the  matter  of  the  first 
element,  and  have  no  other  motion  than  that  which  is  im- 
parted by  the  motion  of  the  fluid  in  which  it  rests.  It 
would  thus  become  a  planet  revolving  in  a  fixed  orbit.  It 
follows  that  the  original  space  in  which  our  present  solar 
vortex  exists  contained  seventeen  or  more  vortices,  the 
central  bodies  of  which  by  becoming  weakened,  were  sub- 
dued successively  by  the  predominating  vortex  of  our  sun, 
and  approached  or  retired  to  the  positions  in  which  their 
forces  were  in  equilibrium  with  those  of  the  surrounding 
globules.  Some  of  these  planetary  centres,  while  yet  they 
were  suns,  were  of  such  mass  that  they  exerted  a  more 
powerful  influence  than  our  sun,  upon  the  vortices  in  their 
neighborhood;  and  thus  certain  minor  vortices  ranged 
themselves  about  Saturn,  Jupiter  and  the  earth,  while  all 
the  others  took  at  once,  suitable  positions  in  the  solar  vor- 
tex. Subsequently,  the  vortices  of  Saturn,  Jupiter  and 
the  earth,  yielding  to  the  superior  power  of  the  sun,  sank 
to  their  several  places  of  equilibrium.  The  vortices  became 
extinct,  and  the  bodies  moved  as  planets  about  the  sun. 
The  central  bodies  of  still  other  vortices,  if  more  than 
seventeen  existed  within  the  present  solar  vortex,  passed 
away  in  right  lines  out  of  the  solar  vortex  and  became 
comets. 

It  follows  from  this  theory  that  the  denser  bodies  of  our 
system  are  those  more  remote  from  the  sun.  For  a  similar 
reason  the  moon  turns  constantly  the  same  side  toward  the 
earth,  because  the  opposite  side  possesses  the  greatest 
density.  The  planets  rotate  on  their  axes  because  they 
were  once  lucid  stars,  the  centres  of  vortices.  Even  now, 
the  matter  of  the  first  element,  collected  at  their  centres, 
continues  its  gyratory  motion  and  acts  on  the  planets. 

Finally,  the  centres  of  the  planets  must  be  subject  to 
irregularities  of  the  same  meaning  as  those  which  charac- 
terize all  natural  things.  All  the  bodies  in  the  universe 


558  PRE-KANTIAN    SPECULATIONS. 

are  relatively  contiguous  to  each  other,  and  act  upon  each 
other.  The  motion  of  each  is  varied  in  innumerable  ways. 
Hence,  though  all  the  planets  approach  a  circular  motion, 
in  a  common  plane,  none  of  them  attain  completely  to 
these  conditions. 

This  fanciful,  arbitrary  and  really  indefensible,  but  most 
ingenious  theory  commanded  a  wonderful  degree  of  cred- 
ence and  respect,  and  even  contended,  on  the  continent,  with 
the  Newtonian  theory  of  universal  gravitation  for  accept- 
ance as  an  adequate  explanation  of  planetary  phenomena. 

§  4.    THE  THEORY  OF  LEIBNITZ.* 

1.  His  Protoffcea. —  The  daring  conception  of  a  primi- 
tive molten  world  was  clearly  formed  by  Leibnitz.  When 
once  this  thought  was  entertained  as  even  a  speculative 
doctrine,  it  was  easy  to  push  beyond  to  the  conception  of 
a  world  heated  to  volatilization,  and  a  whole  svstem  in  a 
state  of  incandescent  vapor,  or  at  least  of  dissociated 
particles  in  some  such  condition  as  Descartes  had  postu- 
lated. The  mental  process  by  which  Leibnitz  advanced 
toward  the  full  acceptance  of  the  vortical  planetary  the- 
ory, appears  from  some  passages  in  his  Protogcea^  which 
I  here  translate: 

"§  II.  It  pleases  the  wise  hands  of  nature  that  the  globe  of  the 
earth,  like  all  created  things,  should  exist  in  a  regular  form;  for 
God  does  not  make  things  without  method;  and  whatever  is  pro- 
duced per  se  [by  progress  from  earlier  to  later  conditions.  A.  W.] 
either  grows  insensibly  particle  by  particle,}:  or  is  fashioned  byselec- 

*Lc  grand  Leibnitz  lui-meme  s'amusa  a  faire,  conune  Descartes,  de  la 
terro  tin  soleil  eteiut,  nn  globe  vitrifle,  sur  leqnel  les  vapours,  c'tant  retombees 
de  son  refroidissement,  formerent  des  mers  qui  dcfposerent  ensuite  les  terrains 
calcaires.— Cuvier:  Discours  sur  les  Revolutions  de  la  Surface  du  Globe,  45, 
Paris,  1828. 

t  Leibnitz:  Protogaxt,  sive  de  prima  facie  Telluris,  etc.,  first  published 
entire  in  1749.  An  abstract,  however,  was  published  in  Acta  Eruditornin,  Leip- 
zig, 1683,  to  which  later  contributions  were  continued  till  1689. 

*  InsensibUUer  aut  concresdt  per  particulas.  Here  we  have  the  "  principle 
of  continuity"  applied  to  the  changes  of  the  material  world. 


THE   THEORY    OF   LEIBNITZ.  559 

tion  and  conflict  of  the  parts  in  effecting  arrangements  among  them- 
selves.* Hence  the  asperity  of  the  mountains  which  roughen  the 
face  of  the  earth  supervened  on  .a  primitive  condition.  And  assur- 
edly, if  the  earth  could  be  conceived  as  liquid  in  the  beginning,  it 
should,  of  necessity,  be  also  symmetrical.  But  it  agrees  with  the 
general  laws  of  bodies  that  solid  substances  should  consolidate  from 
liquid.  This  is  evidenced  from  solids  found  inclosed  in  solids,  cer- 
tain layers  and  nuclei  being  very  often  rounded  off  at  their  angles 
and  limits,  and  veins  being  frequently  observed  in  rocks,  and  gems 
in  stones.  But  also  numerous  relics  of  ancient  things  everywhere 
exist  —  plants  and  animals,  and  things  artistically  fashioned  into  a 
novel  and  stony  similitude.  It  follows  that  what  we  now  recognize 
as  hard  is  a  later  formation ;  it  must,  therefore,  have  been  originally 
fluid.  Ultimately,  fluidity  itself  results  from  internal  motion,  and, 
as  it  were,  from  some  degree  of  heat.f  This  is  shown  by  experi- 
ments. For  even  with  undiminished  heat,  water  becomes  glass, 
while,  on  the  contrary,  corrosive  fluids,  strong  through  some  hidden 
motion,  are  with  difficulty  congealed.  But  heat  or  internal  motion 
is  from  fire  or  light;  that  is,  a  pervading  subtile  spirit.  Thus,  we 
arrive  at  the  moving  cause,  whence,  also,  Sacred  History  derives  the 
beginning  of  its  cosmogony. 

§  III.  As  far,  therefore,  as  human  knowledge  is  able  to  reach, 
either  by  ratiocination  or  by  the  teaching  and  tradition  of  the  Sacred 
Scriptures,  the  first  step  in  the  formation  of  things  is  the  separation 
of  light  and  darkness,  that  is  of  things  active  and  things  passive ; 
the  second  is,  the  discrimination  of  things  passive  among  themselves, 
that  is,  the  separation  of  things  liquid  from  things  dry;  which  two 
are  distinguished,  among  things  passive,  according  to  their  different 
power  of  resistance  and  degree  of  firmness.  Thus  bodies  are  vari- 
ously transformed  by  fires  and  floods.  Moreover,  the  things  which 
we  see  opaque  and  dry  were  in  the  beginning  ignited;  then,  after  a 
time,  being  exhausted  of  their  waters,  the  elements  were  separated, 
and,  as  we  may  believe,  the  present  aspect  of  the  world  emerged. 
The  facts  according  with  these  views  certain  priests  of  wisdom  build 
into  the  form  of  a  hypothesis,  and  explain  more  distinctly  the 
method  of  separation.  Namely,  that  certain  vast  globes  of  the  uni- 
verse were  brought  into  existence,  which  then  either  shone  by  their 

*Autpro  sese  disponentium  delectu  conflictuque  tornatur.  Here  is  a  distinct 
statement  of  the  principle  of  "natural  selection." 

t  POTTO  ipsa  fluiditas  ab  intestino  est  motu;  et  tanquam  gradu  caloris  It  is 
interesting  to  note  here  also  a  plain  statement  of  the  modern  "mechanical 
theory  of  heat." 


560  PRE-KANTIAN   SPECULATIONS. 

own  light,  according  to  the  fashion  of  a  fixed  star  or  our  own  sun, 
or  were  projected  from  a  sun  of  their  own,  their  matter  being  subse- 
quently boiled  out  and  spumescent,  and  scoriae  issuing  forth  through 
fusion  —  a  condition  of  matter  perhaps  analogous  to  that  in  the 
spots  which  dim  the  light  of  our  sun,  and  which  the  ancients  some- 
times denied  him,  though  they  recognized  a  feeble  obscuration,  but 
which  the  optical  instruments  discovered  in  our  age  enable  us  to 
study.  By  excess,  however,  of  accumulated  material,  the  internal 
heat  was  overcome,  and  a  cooled  crust  was  formed  surrounding  the 
body.  Thence  came  into  existence  the  dark  star,  shining  by  reflected 
light,  like  the  planets.  That  we  inhabit  such  a  Vulcan  they  either 
suppose  or  pretend  to  be  established  by  that  Mosaic  separation  of 
light  and  darkness.  It  is,  indeed,  believed  by  most  people,  and  is 
also  intimated  by  the  sacred  writers,  that  a  store-house  of  fire  is 
established  in  the  interior  of  the  earth,  which  at  some  time  will  again 
burst  forth.  This  conjecture  is  confirmed  by  the  vestiges  of  the 
primitive  aspect  of  nature  which  still  remain.  For  every  scoria  from 
fusion  is  a  kind  of  glass.  But  the  crust  ought  to  resemble  scoria, 
for  this  covered  the  fused  matter  of  the  globe  as  in  a  furnace  of 
metal,  and  became  hardened  after  fusion.  That  such,  indeed,  is  the 
surface  of  our  globe  (for  it  is  not  given  us  to  penetrate  further)  we 
actually  experience.  For  all  earths  and  stones  return  to  glass  by  the 
agency  of  fire,  and  so  much  the  more  as  they  approach  nearer  the 
nature  of  a  rude  rock.  Neither,  meanwhile,  would  I  deny  that 
earthy  and  vitreous  products  may  possibly  be  born  from  waters 
through  transformations  of  a  higher  order;  since  it  is  evident  that 
the  waters  are  pregnant  with  various  bodies,  and  that  matter  itself, 
everywhere  similar  to  itself,  is  able  per  se  to  assume  some  certain 
form.  Nor  are  there  any  ultimate  unchangeable  elements.  But  it 
is  sufficient  for  us  in  this  place,  that  by  human  art,  through  the 
efficient  agency  of  fire,  earthy  matters  become  converted  into  glass. 
The  great  bones  of  the  earth  themselves,  those  naked  rocks  and 
eternal  flints,  what,  since  everything  passes  very  nearly  into  glass, 
are  they,  unless  consolidated  from  bodies  formerly  fused  by  that 
great  primitive  force  which  fire  has  hitherto  exerted  over  facile  mat- 
ter? For  this,  surpassing  by  an  enormous  excess  the  power  of  our 
furnaces  and  their  degree  of  duration,  what  wonder  is  it  if  it  then 
produced  results  which  men  are  unable  to  imitate,  although  art  daily 
advances,  and  continually  produces  things  new  and  unheard-of,  yes, 
indeed,  brings  bodies  fused  by  its  own  fire  sometimes,  to  a  high  de- 
gree of  hardness.  When,  therefore,  all  substances  which  are  not 


THE   THEORY    OF   LEIBNITZ.  561 

dissipated  in  vapors  are  at  length  fused,  and,  especially  through  the 
power  of  burning  lenses,  assume  the  nature  of  glass,  it  is  easy  to 
understand  that  glass  is,  as  it  were,  the  basis  of  the  earth ;  and  that 
its  nature  lies  concealed  under  the  masks  of  very  many  other  bodies, 
its  particles  being  variously  corroded  and  elaborated,  partly  by 
solution  and  agitation  of  waters,  partly  by  repeated  elevations  in 
vapor  and  distillations,  until  finally  by  the  aid  of  salts  added  to  the 
power  of  heat,  stony  hardness  is  reduced  to  mud  suited  for  nourish- 
ing plants  and  animals,  and  is  even  reduced  also,  to  a  volatile  nature. 
Meantime,  by  as  much  as  anything  in  the  earth  is  more  nude  and 
primitive,  and  approximated  to  the  simple  constitution  of  rocks, 
this  the  more  persists  in  the  fire,  though  it  is  fused  by  the  highest 
heat,  and  finally  vitrifies.  For  even  a  calcareous  rock  which  resists 
our  furnaces  is  reduced  to  glass  by  the  speculum.  Even  as  to  sand, 
which  is  a  large,  and  at  the  same  time  the  simplest  portion  of  the 
earth,  and  fills  immense  deserts  and  shores,'  and  the  bottom  of  the 
sea,  and  underlays  the  better  soil  with  gravel,  to  what  can  it  be  re- 
ferred on  examination,  more  properly  than  to  stones  or  translucent 
fluors,  and,  as  it  were,  glass,  by  motion  either  in  a  state  of  fusion 
or  by  other  means,  reduced  to  small  fragments  ?  —  a  result  also  easily 
produced  by  fire  if  salts  are  present,  and  these  have  never  been 
wanting  from  the  beginning. 

§  IV.  From  this  genesis  of  things  comes  the  origin  of  the  salt 
sea  observed  to-day.  For  as  things  burned  out  attract  moisture 
after  cooling,  whence  oils  are  produced  by  chemists  by  means  of  lixi- 
viation,  so  it  appears,  in  the  beginning  of  things,  while  our  globe 
was  yet  incandescent  and  the  opaque  was  not  yet  separated  from  the 
light,  moisture,  being  expelled  by  fire,  was  not  present  in  the  atmos- 
phere; but  subsequently  reproduced  by  a  true  process  of  distillation, 
it  was'again  condensed  into  watery  vapors  through  abatement  of  the 
heat;  and  when,  by  the  cooling  of  the  terrestrial  surface,  the  mass 
became  absorbed,  it  was  finally  returned  in  water,  which  bathing  the 
face  of  the  earth  —  the  wide  remains  of  the  recent  burning  —  re- 
ceived fixed  salt  in  itself.  Hence  originated  a  sort  of  lixivium 
which  flowed  together  in  the  sea.  Indeed,  from  the  analysis  of 
plants,  as  has  been  noted  from  the  observations  of  the  Parisian  Aca- 
demicians, we  have  learned  that  two  fixed  salts  remain  in  lixivia  — 
the  one  alkaline,  as  the  artisans  express  it,  the  name  being  derived 
from  a  plant  which  our  people  call  soda,  and  the  Arabes  cali.  the 
other  marine,  and  more  inclined  to  acid.  Lastly,  it  may  be  sup- 
posed that  the  crust,  contracting  through  cooling,  as  among  metals 
36 


562  PRE-KANTIAN    SPECULATIONS. 

and  other  substances  which  by  fusion  become  more  porous,  left  bub- 
bles, great  according  to  the  magnitude  of  the  thing,  that  is,  cavities 
under  vast  arches,  inclosed  in  which  was  air  or  humor;  that  then 
also  certain  matters  separated  in  layers,  and  that  through  variation 
of  material  and  of  temperature,  masses  subsided  unequally,  so  that  on 
every  hand,  disruptions  occurred,  the  fragments  being  tilted  in 
valley  slopes,  while  the  solider  parts,  like  columns,  held  the  highest 
place.  Thus,  therefore,  mountains  came  into  existence.  The  weight 
of  the  waters  was  added  for  preparing  a  basin  in  the  still  soft  bottom. 
At  length,  either  through  weight  of  material  or  force  of  elastic 
vapors,  the  immense  arches  were  broken ;  the  humor  in  the  cavities 
being  expelled  through  the  ruins  or  flowing  spontaneously  from  the 
mountains,  inundations  followed,  which  thus  again  deposited  sedi- 
ments by  intervals;  and  these  hardening,  and  presently  a  similar 
cause  returning,  diverse  strata  were  laid  down  one  upon  another, 
and  so  the  face  of  the  orb  as  yet  tender,  was  many  times  renewed. 
At  length,  these  causes  becoming  quiet  and  equilibrated,  a  more  per- 
sistent state  of  things  emerged.  Whence  now,  a  duplex  origin  of 
solid  bodies  is  intelligible  —  one  when  they  solidify  from  fusion  by 
fire,  the  other  when  they  consolidate  from  solution  in  water.  It  is 
not  therefore  to  be  supposed  that  stones  arise  from  fusion  alone. 
That  this  is  most  possible  from  the  first  mass  and  basis  of  the  earth, 
I  admit.  Nor  do  I  doubt  that  afterward,  when  liquid  matter  flowed 
over  the  surface  of  the  earth,  after  the  return  of  quiet,  a  great  vol- 
ume of  materials  was  deposited  from  the  eroded  rubbish,  of  which 
some  formed  various  kinds  of  earth,  others  hardened  into  rocks. 
Among  these,  diversified  strata  in  regular  order  of  superposition  tes- 
tify to  the  various  recurrences  and  intervals  of  precipitation. 

§  V.  These  things  may  perhaps  be  said  without  dissent  con- 
cerning the  cradle  of  our  orb;  and  they  contain  the  germs  of  a  new 
science  which  might  be  designated  Natural  Geography;  we  venture, 
however,  rather  to  suggest  it  than  to  construct  it.  For,  although 
the  sacred  monuments  of  the  divine  oracles  favor,  we  nevertheless 
defer  judgment  to  those  with  whom  is  the  right  of  interpretation. 
And  although  the  vestiges  of  the  ancient  world  are  united  in  the 
present  aspect  of  things,  nevertheless,  posterity  will  define  every- 
thing more  correctly,  when  the  curiosity  of  mortals  shall  have  pro- 
ceeded so  far  as  to  describe  the  kinds  of  soil  and  the  rocky  strata 
extending  through  wide  regions.  But  indeed,  I  do  not  impute  all 
inequalities  of  the  earth  or  the  nature  of  the  sea  bottom  to  primitive 
solidification.  It  suffices  to  have  deduced  by  general  causes, 


THE   THEORY    OF    LEIBNITZ.  563 

the  skeleton  itself,  and,  as  it  were,  the  bones  of  the  earth's  exte- 
rior, and  the  sum  of  its  entire  structure.  For  these  seem  to  be  the 
true  sources,  if  you  seek  them,  whence  the  immense  cavity  of  the 
ocean  has  been  derived,  and  the  monstrous  masses  of  the  mountains, 
as  for  instance,  *  *  *  But  I  do  not  thus  deny  that  the  globe, 
being  now  solid,  minor  conflagrations  and  motions  of  the  earth,  and 
limited  inundations,*  and  sedimentations  from  standing  waters, 
have  supervened,  which  have  often  taken  possession  of  extensive 
tracts  and  transformed  them;  for  of  these  the  vestiges  which  still 
remain  with  us  will  presently  be  described.  Nor  is  it  doubtful  that 
straits  have  been  cut  by  incursions  of  the  sea ;  that  lands  have  been 
absorbed  in  the  abyss  or  transformed  into  morasses;  that  shores 
have  now  been  inundated,  now  uncovered ;  that  lower  places  have 
been  depressed,  and  narrows  shut  up  by  the  ruins  of  mountains  and 
the  obstruction  of  the  courses  of  the  waters ;  that  by  turns  lakes  burst- 
ing through  outlets  violently  opened,  have  excavated  valleys  for 
their  discharge;  that  volcanic  mountains  have  been  opened  and 
closed ;  that  pumices  have  been  spread  far  and  wide,  and  the  marks 
of  conflagrations  indelibly  impressed.  But  what  ought  to  be  in- 
ferred from  causes  acting  on  a  larger  or  smaller  scale,  posterity  will 
sometime  more  easily  determine,  after  the  home  of  the  human 
species  shall  have  been  more  thoroughly  explored,  "f 

We  find  here  very  definitely  enunciated,  the  germs  of 
modern  geological  theory.  A  few  of  Leibnitz'  contempo- 
raries, more  especially  Steno,  had  already  expressed  a 
rudimentary  conception  of  the  agency  of  the  sea  in  the 
deposition  of  fossil  remains;  but  Leibnitz  was  the  first  to 
sugg-est  the  full  extent  of  igneous  action,  and  thus  fur- 
nished the  basis  for  the  famous  Plutonic  theory  which 
divided  opinion  a  century  later.  More  conservative,  how- 
ever, than  the  Plutonists,  he  united,  as  modem  geology 
does,  the  principle  of  aqueous  action  with  that  of  igneous 
action;  and  deserves  to  be  counted  one  of  the  most  philo- 
sophic and  far-seeing  among  the  founders  of  the  science. 

*  Priuatas  duuiones. 

t  Most  of  the  remainder  of  the  Protogsea  is  devoted  to  accounts  of  caverns, 
metallic  ores,  gems  and  other  minerals,  with  quite  extended  descriptions  of  fos- 
sil remains,  the  whole  accompanied  by  eleven  very  good  copperplates  of  illus- 
trations. 


564  PRE-KANTIAN    SPECULATIONS. 

Let  us  glance  now  more  particularly  at  his  cosmogonic 
views,  which,  so  far  as  his  own  thought  is  concerned,  were 
the  logical  outcome  of  his  geology. 

2.  His  Planetogeny. —  The  Cartesian  theory  com- 
manded the  general  approval  of  Leibnitz;  arid  his  opin- 
ions were  published  as  early  as  1680,*  in  an  essay  on  the 
causes  of  the  celestial  motions.  He  assumes  that  every 
body  immersed  in  a  fluid  and  moving  in  a  curved  line 
must  be  acted  upon  by  the  fluid  itself.  For  a  body  mov- 
ing in  a  curve  tends  continually  to  take  the  direction  of  a 
tangent,  and  would  do  so  if  there  were  nothing  to  restrain 
it.  But  nothing  can  restrain  it  unless  contiguous  to  it; 
and  in  a  fluid  there  is  nothing  contiguous  except  the  fluid 
itself.  It  follows,  therefore,  that  the  fluid  must  possess 
the  same  motion  as  the  body.  This  reasoning  applies  to 
the  planets. 

As  the  planets  revolve  about  the  sun  according  to  the 
law  of  equal  areas,  the  "  ether  or  fluid  orb  of  each  planet " 
must  move  according  to  the  same  law.  This  will  be  the 
case  if  we  conceive  the  fluid  to  consist  of  an  infinitude  of 
concentric  circles,  each  revolving  with  a  velocity  inversely 
proportional  to  its  distance  from  the  sun.  A  circulation 
of  this  kind  is  termed  harmonic.  The  actual  motion  of  a 
planet  is  something  more  than  this,  since  it  moves  with 
unequal  velocity  and  at  a  varying  distance  from  the  sun. 
It  must,  therefore,  be  actuated  also  by  a  paracentric  force, 
oy  virtue  of  which  it  approaches  and  recedes  from  the 
sun.  But,  in  approaching'  the  sun,  its  velocity  is  acceler- 
ated because  then  immersed  in  a  fluid  having  a  more  rapid 
vortical  movement,  and  in  receding  from  the  sun  its 
velocity  must  be  retarded  until  it  accords  with  that  of  the 
zone  of  the  fluid  to  which  it  has  attained.  "Consequently, 
the  harmonic  proportion  holds  not  only  in  arcs  of  circles, 
but  in  describing  any  other  curve,"  since  the  minute  arc 

*  Acta  Eruditorum,  Leipzig,  1680. 


THE   THEORY    OF   LEIBNITZ.  565 

described  in  each  infinitesimal  element  of  time  is  essen- 
tially identical,  whatever  the  form  of  the  curve. 

The  paracentric  motion  is  composed  of  two  factors; 
one  is  the  tangential  tendency  which  the  planet  must 
experience  even  when  swimming  in  and  with  a  fluid;  the 
other  is  the  sun's  attraction,  or  rather  the  planet's  gravity.* 
Since  we  know  that  each  planet  revolves  in  an  ellipse  with 
the  sun  in  one  focus,  and  with  a  velocity  according  to 
the  law  of  equal  areas;  and  since  no  law  of  circulation 
but  the  harmonic  will  afford  the  necessary  conditions  for 
this,  it  follows  that  we  must  seek  a  law  of  gravity,  which, 
combined  with  the  tangential  tendency,  will  constitute 
such  paracentric  motion  as  in  connection  with  the  har- 
monic will  carry  the  planet  along  the  perimeter  of  an 
ellipse,  f  This  law  he  demonstrates  and  enunciates  as 
follows:  "If  a  heavy  body  be  carried  in  an  ellipse,  or 
any  other  conic  section,  with  a  harmonic  circulation,  and 
the  centre,  both  of  attraction  and  circulation,  be  in  the 
'  focus  of  the  ellipse,  then  the  attractions  or  solicitations  of 
gravity  will  be  as  the  squares  of  the  circulations  directly, 
or  as  the  squares  of  the  radii  or  distances  from  the  focus 
reciprocally."  This,  it  will  be  observed,  is  precisely  the 
law  of  gravitation  previously  announced  by  Newton  and 
noticed  in  the  Acta  Eruditorum  at  Leipzig. 

Leibnitz  confesses  that  he  is  not  prepared  to  indicate 
what  motion  of  the  ether  it  is  which  imparts  that  tendency 
called  gravitation, J  nor  what  causes  the  relation  of  differ- 
ent planets  expressed  by  saying  that  the  squares  of  their 

*  Such  an  expression  is  employed  at  the  same  time  that  Leibnitz  opposes 
the  Newtonian  theory.  Thi*  tendency  here  called  attraction  is  (perhaps  disin- 
genuously) ascribed  to  some  impulse  received  from  the  ambient  fluid,  as  from  a 
magnet. 

tSome  later  Cartesians,  as  John  Bernoulli!,  conceived  a  way  of  producing 
elliptic  motion  in  a  circular  vortex. 

tThe  successors  of  Leibnitz  and  Descartes  thought  they  had  discovered 
a  means  of  constructing  a  vortex  so  as  to  produce  a  tendency  of  bodies  to  the 
centre. 


566  PRE-KANTIAN    SPECULATIONS. 

periodic  times  are  as  the  cubes  of  their  mean  distances 
from  the  sun. 

One  of  the  most  obvious,  as  also  most  fatal,  of  the 
objections  to  these  vortical  theories,  is  the  fact  that  in 
spite  of  the  power  of  the  fluid  to  carry  the  masses  of  the 
planets  in  a  uniform  direction,  the  tenuous  comets  pass 
through  it  unhindered  and  undeflected,  and  in  all  imagin- 
able directions,  and  travel  at  the  same  time,  like  the 
planets,  with  velocities  regulated  by  the  law  of  equal 
areas.  * 

§  5.  THE  VORTICAL  THEORY  OF  SWEDENBORG. 

In  1733-4,  Emanuel  Swedenborg,  a  Swedish  philoso- 
pher, during  a  sojourn  abroad,  published  a  remarkable 
work  on  the  Principles  of  Things,  in  which  a  vortical 
theory  was  set  forth  which  in  many  respects  was  original 
and  seems  to  be  less  amenable  to  certain  objections  than 
the  theories  of  his  predecessors.!  The  exposition  of 

*The  reader  may  find  these  theories  discussed  in  Gregory's  Astronomia 
Elementa  [or  Elements  of  Astronomy,  Physical  and  Geometrical,  1701].  Objec- 
tions to  the  admission  of  an  interplanetary  fluid  are  extensively  urged  by  Cotes 
in  his  Preface  to  Newton's  Prlncipia.  On  the  conflict  between  Cartesianism 
and  the  Newtonian  philosophy,  sea  Whewell:  History  of  the  Inductive  Sciences, 
Am.  ed.,  i,  429-32. 

t Emanuel  Swedenborg:  Principia  Rerum  Naturalium.  Dresden  and  Leip- 
zig, 1733-4,  3  vols.  folio.  [First  Principles  of  Natural  Things,  being  new  at- 
tempts toward  a  Philosophical  Explanation  of  the  Elementary  World.]  This 
was  produced  in  elegant  style,  with  copious  engravings,  at  the  expense  of  the 
Duke  of  Brunswick.  I  have  not  seen  the  original  work,  nor  is  a  translation  of 
it  included  among  the  translations  published  by  the  "American  Swedenborg 
Printing  and  Publishing  Co.,"  New  York,  1875;  but  through  the  kindness  of  Mr. 
T.  F.  Wright,  one  of  the  editors  of  the  New  Jerusalem  Magazine,  of  Boston,  I 
have  been  favored  with  the  loan  of  a  translation  of  the  first  volume,  made  by 
Rev.  Augustus  Clissold,  M.  A.,  and  published  in  London,  in  1846.  As  Sweden- 
borg is  principally  known  as  a  mystical  writer  on  religious  and  theological  sub- 
jects, it  has  been  customary  to  pass  by  his  scientific  speculations  as  not  having 
been  based  on  any  just  and  adequate  apprehension  of  physical  principles. 
Whether  the  charge  be  merited  or  not,  we  are  interested  in  knowing  what  his 
views  were.  Moreover,  Swedenborg  did  not  retire  from  public  and  professional 
life  to  enter  upon  his  course  of  theological  meditation  and  study,  until  at  the  age 
of  57,  which  was  eleven  years  after  the  publication  of  his  Principia.  Dunng 
his  professional  career  he  was  ranked  as  one  of  the  most  eminent  scientists  of 


THE   VORTICAL   THEORY    OF   SWEDENBORG.  567 

his  theory  is  prolix  and  abstruse  in  an  eminent  degree  ; 
and  a  casual  reader  not  possessed  of  a  suitable  cast  of 
mind  would  pronounce  it  full  of  paradoxes  and  contradic- 
tions. Assuming,  however,  that  the  author  must  have 
possessed  a  logical  apprehension  of  the  things  of  which 
he  wrote,  I  h?,ve  educed  and  condensed  the  essence  of  his 
theory  in  the  following  statement. 

The  first  cause  is  the  infinite  or  unlimited.  This  gives 
existence  to  the  first  finite  or  limited.  That  which  pro- 
duces a  limit  is  analogous  to  motion.  The  limit  produced 
is  a  point,  the  essence  of  which  is  motion  ;  but  being 
without  parts,  this  essence  is  not  actual  motion  but  only 
a  conatus  to  it.  From  this  first  proceed  extension,  space, 
figure  and  succession  or  time.  As  in  geometry  a  point 
generates  a  line,  a  line  a  surface,  and  a  surface  a  solid,  so 
here  the  conatus  of  the  point  tends  toward  lines,  surfaces 
and  solids.  In  other  words,  the  universe  is  contained  in 
ovo  in  the  first  natural  point. 

The  motion  toward  which  the  conatus  tends  is  circular, 
since  the  circle  is  the  most  perfect  of  all  figures,  and 
tendency  to  motion,  impressed  by  the  Infinite,  must  be 
tendency  to  the  most  perfect  figure.  "  The  most  perfect 
figure  of  the  motion  above  described  must  be  the  per- 
petually circular ;  that  is  to  say,  it  must  proceed  from 
the  centre  to  the  periphery  and  from  the  periphery  to 
the  centre.  *  *  *  It  must  necessarily  be  of  a  spiral 
figure,  which  is  the  most  perfect  of  all  figures.  In  the 
spiral  there  is  nothing  but  what  partakes  of  a  certain 

Sweden,  and  of  Europe,  enjoying  the  society  and  patronage  of  the  first  officials, 
and  of  the  princes  and  rulers  of  several  countries.  Especially  was  he  known  as 
a  mathematician  and  mechanician.  He  wrote  also  on  astronomy,  physics,  min- 
eralogy and  monetary  science.  He  was  offered  the  chair  of  pure  mathematics 
in  the  University  of  Upsal,  but  declined;  was  a  corresponding  member  of  the 
Academy  of  Sciences  of  St.  Petersburg,  and  one  of  the  earliest  members  of  the 
Royal  Academy  at  Stockholm,  where  his  portrait  hangs  near  that  of  Linnseus,  as 
one  of  the  past  presidents  of  the  Academy. 
*  Clissold's  translation,  i,  63. 


568  PRE-KANTIAN    SPECULATIONS. 

kind  of  circular  form  ;  and  nothing  within  it  is  put  into 
motion  but  what  takes  a  circular  direction.  The  motion 
proceeds  perpetually  to  a  circle.  The  spiral  motion  may 
be  said  to  be  infinitely  circular  ;  every  motion  around  the 
centre  is  a  circle  ;  its  progression  toward  the  periphery 
is  circular  [curvilinear?];  in  a  word,  its  figure  is  circular 
[curvilinear?]  in  all  its  dimensions  and  bearings.  Per- 
petual circulation  is  the  same  as  a  perpetual  spiral ;  hence 
the  most  perfect  figure  of  motion,  as  well  in  conatus  as 
in  act,  can  be  conceived  to  be  no  other  than  the  perpetual 
spiral,  winding,  as  it  were,  from  the  centre  to  the  peri- 
phery, and  again  from  the  periphery  to  the  centre  ;  thus 
it  is  a  perpetual  reciprocation  and  spiral  fluxion."  * 

But  all  this  conatus  and  possibility  of  motion  exists  as 
yet  only  in  a  metaphysical  sense.  There  is  no  actual 
motion.  "  Before  anything  can  be  produced,  conatus 
must  pass  into  act  ;  like  what  is  formal  into  what  is  real ; 
and,  consequently,  the  point  must  pass  with  its  conatus 
into  motion."  f  Motion,  however,  is  the  only  medium  by 
which  anything  new  can  be  produced.  Motion,  itself, 
which  is  merely  a  quality  and  a  mode,  and  nothing  sub- 
stantial, may  yet  exhibit  something  substantial,  or  the  re- 
semblance of  what  is  so,  provided  there  be  anything  sub- 
stantial put  into  motion."  \  Now,  if  an  infinitely  small  par- 
ticle be  set  in  infinitely  rapid  motion  by  a  spiral,  it  may  be 
made  to  generate  a  line,  a  surface,  or  a  solid,  by  suitable 
species  of  motion  ;  and  thus  a  "simple  finite  or  first  sub- 
stantial" would  be  originated.  As  the  simple  finite  de- 
rives its  existence  from  the  motion  in  the  primitive 
conatus,  it  will  have  an  actual  spiral  motion.  Thus  the 
potential  becomes  actual.  The  simple  finite  is  an  epitome 

*  Op.  cit.  63-4.   Compare  also,  p.  82,  speaking  of  finites.    I  leave  it  for  others 
to  explain  the  legitimacy  of  confounding  circles  and  spirals. 

t  Op.  cit.,  66. 

*  Op.  cit.,  68. 


THE   VORTICAL   THEORY    OF   SWEDENBORG.          569 

of  the  world.*  It  fills  space,  but  is  minute  beyond  con- 
ception. It  is  endowed  with  figure.  All  its  characters 
are  exactly  repeated  in  other  finites.  Possessing  the  same 
active  force  as  the  point,  "it  is  able  to  finite  and  produce 
the  subsequent  and  more  compounded  finites."  f  Thus 
compounds  arise. 

The  motion  in  the  finite  is  spiral  and  reciprocal,  like 
that  conative  in  the  point.  This  spiral  motion  determines 
the  position  of  two  poles,  and  these  assume  the  form  of 
cones.  With  poles  are  coordinated  "  an  equator,  ecliptic 
meridians  and  other  perpendicular  circles."  \  The  finite, 
from  its  inherited  conatus,  develops  "a  progressive  motion 
of  all  the  parts  and  spires."  Moreover,  since  the  centre 
of  the  spiral  is  not  coincident  with  the  centre  of  gravity 
of  the  corpuscle,  the  latter  is  rotated  and  constrains  the 
corpuscle  to  a  local  motion.  "  Therefore,  not  only  all  the 
primitive  force  in  the  point,  but  that  also  which  is  derived 
into  its  sequents  consists  in  this:  that  the  motion,  state  or 
conatus  in  a  point  tends  to  a  spiral  figure.  This  motion, 
state  and  conatus  cause  an  axial,  and  at  the  same  time,  a 
progressive  motion.  These  together  produce  another  or 

*  This  account  of  the  origin  of  a  substantial  particle  seems  to  proceed  on 
the  principle  of  the  infinitesimal  calculus.  Granted  the  infinitesimal  matter, 
masses  of  matter  are  the  necessary  derivative.  The  infinitesimal  finite  seems 
to  be  assumed  for  a  starting  point  in  order  to  get  as  near  as  possible  to  a  concep- 
tion congeneric  with  that  of  the  original  point,  which  is  only  conatus.  But  be- 
tween an  atom  of  real  matter  and  the  absolute  negation  of  matter  in  the  point, 
is  a  chasm  which  does  not  seem  to  be  bridged.  Boscovich,  who  wrote  in  1756 
( T/ieoria  philosophic?  naturalis  redacta  ad  unlearn  legem  viriiim  in  natura  exis- 
tentium),  escaped  this  difficulty  by  assuming  that  the  atom  was  not  extended, 
though  possessed  of  mass  —  a  mere  centre  surrounded  by  spheres  of  repulsion 
and  attraction.  Sir  William  Thomson  has  propounded  also,  a  dynamical  theory 
of  atoms  (On  Vortex  Atoms,  Proc.  Roy.  Soc.  Edinboro1,  18  Feb.,  1867)  in  which 
the  "  vortex  ring"  of  Helmholtz  is  made  the  type  of  an  atomic  ring  formed  of 
a  primitive  fluid  perfectly  incognizable  except  in  this  vortical  mode  of  motion. 
The  analogy  of  this  to  the  vortical  "first  finite"  of  Swedenborg  is  apparent, 
though  an  important  difference  exists  in  the  use  of  a  primitive  fluid  by  Sir  W. 
Thomson. 

t  Op.  dt.,  79. 

•«•  Op.  (At.,  86. 


570  PRE-KANTTAN    SPECULATIONS. 

a  local  motion,  a  motion  in  which  consists  the  active 
power  of  finiting  and  compounding  the  sequents,  and  of 
modifying  them  throughout  a  lengthened  series  in  the 
manner  in  which  we  perceive  by  our  senses,  the  world  at 
large  to  be  modified."  * 

The  world  and  the  solar  system  are  conceived  as  evolved 
through  the  continuance  and  enlargement  of  the  processes 
mentioned  above  as  in  their  incipiency.  It  would  be  too 
tedious  for  the  reader  to  be  conducted  through  the  several 
hundred  pages  in  which  the  author  discourses  of  "  second 
finites"  and  "third"  and  "fourth  finites,"  "actives" 
and  "  substantials."  Suffice  it  to  say  that  the  solar 
space  is  a  grand  vortex  ;f  that  it  has  grown  through  the 
concurrence  of  similar  vortices;  that  no  other  force  has 
been  needed  than  the  one  at  the  solar  centre,  while  this 
proceeded  from  the  primitive  point;  J  that  the  sun  is 
stated  to  rotate  on  an  axis;  "that  the  solar  matter  con- 
centrated itself  into  a  belt,  zone  or  ring  at  the  equator  or 
rather  ecliptic;  that  by  attenuation  of  the  ring  it  became 
disrupted;  that  upon  the  disruption,  part  of  the  matter 
collected  into  globes,  and  part  subsided  into  the  sun,  form- 
ing solar  spots;  that  the  globes  of  solar  matter  were  pro- 
jected into  space;  that  consequently  they  described  a 
spiral  orbit;  that  in  proportion  as  the  igneous  matter  thus 
projected  receded  from  the  sun,  it  gradually  experienced 
refrigeration  and  consequent  condensation;  that  hence  fol- 
owed  the  formation  of  the  elements  of  ether,  air,  aqueous 
vapor,  etc.,  until  the  planets  finally  reached  their  present 
orbits;"  §  that  the  process  of  system  building  extended  to 
the  stars,  and  that  the  Milky  Way  is  the  ay  is  of  the 
firmamental  vortex. 

*  Op.  cit.,  91-2. 

tSee,  especially,  Part  III,  ch.  iv.    De  chao  universali  soils  et  planetarum, 
deque  separations  ejus  In  planetas  et  satellites. 
{  Op.  cit.,  203-8. 
§  Rev.  A  Clissold's  Introduction,  p  Ixxxi. 


THE   VORTICAL   THEORY   OF   SWEDEXBORG.  571 

It  will  thus  be  seen  that  Swedenborg's  theory  begins 
with  an  immaterial  point,  like  the  monad  of  Leibnitz; 
that  it  therefore  has  no  inertia  to  be  overcome,  but  is 
gifted  with  an  inherent  force  which  finally  flows  out  into 
actual  motion  and  actual  substance.  Kepler  also  regarded 
the  vortical  medium  as  the  immaterial  emanation  from  the 
sun's  body,  but  the  planets  which  swam  in  it  were  mate- 
rial and  were  floated  as  in  a  material  medium.  According 
to  Swedenborg,  the  planetary  body  is  not  passive,  but 
possesses  an  inherent  conatus  to  motion.  It  is  difficult  to 
perceive  why  Leibnitz,  who  posited  self-moving  monads, 
did  not,  like  Swedenborg,  avail  himself  of  this  mode  of 
energy,  and  thus  escape  the  difficulties  imposed  by  the 
motion  of  inert  bodies,  and  the  presence  of  a  medium 
which,  by  some  mysterious  selection,  bore  the  planets  in 
its  vortex  without  affecting  the  comets. 

The  Swedenborgian  theory  is  not  regarded  as  com- 
pletely set  forth  in  the  Principia.  His  later  works  are 
thought  to  be  "fuller  of  philosophy."  Mr.  Wright,  of  the 
New  Jerusalem  Magazine,  Boston,  has  pointed  out  pas- 
sages which  he  thinks  afford  additional  light.* 

*  These  are  Divine  Love  and  Wisdom,  beginning  at  No.  282,  and  The  True 
Christian  Religion,  Nos.  76  and  78,  especially  No.  78.  I  take  the  liberty  of 
quoting  from  a  letter  of  Mr.  Wright,  what  he  regards  as  the  deeper  significance 
of  these  passages.  "  You  will  there  notice  that  the  idea  is  that  creation  is  by 
the  self-subsisting  God;  that  His  infinite  love  and  wisdom  demanded  the  uni- 
verse; that  its  production  was  not  by  extension  of  the  infinite,  nor  by  the  ex- 
tension of  nothing,  but  by  the  determination  of  the  infinite  into  recipient 
forms  produced  by  itself  by  degrees,  each  of  which  was  the  medium  of  creative 
energy  to  that  next  below;  that  this  process  terminated  in  matter;  that  this 
gradation  was,  is  and  always  will  be  the  vehicle  of  transmission  of  life  from  the 
Divine;  that  the  preservation  exemplifies  the  creation;  that  the  production  of 
forms  of  life  on  earth  was  through  the  production  of  their  spiritual  prototypes, 
when  the  time  came  for  it  in  the  process  of  development;  thus,  that  the  evolu- 
tion was  subject,  at  every  point,  to  the  creative  process.  This  seems  to  us  to  be 
the  whole  view,  of  which  that  in  the  Principia  is  only  a  part."  (Letter  of  Febru- 
ary 24.  1880.) 


572  PRE-KANTIAN   SPECULATIONS. 

§  6.   THE  SPECULATIONS  OP  THOMAS  WRIGHT. 

The  next  prominent  writer  who  put  forth  cosmogonic 
views  worthy  of  comparison  with  later  nebular  theories 
was  Thomas  Wright,  of  Durham.*  Unable  personally  to 
consult  his  writings,  I  am  indebted  to  Kant  for  an  intima- 
tion of  the  nature  of  Wright's  speculations.  In  the  Intro- 
duction to  his  General  History  of  Nature,  he  says:  "  The 
First  Part  is  chiefly  occupied  with  a  new  system  of  world 
structure.  Herr  Wright,  of  Durham,  whose  treatise  I 
first  became  acquainted  with  through  the  Hamburg' schen 
freien  Urtheilen  of  the  year  1751,  gave  me  the  first  sug- 
gestion toward  the  contemplation  of  the  fixed  stars,  not 
as  a  promiscuous  assemblage  without  visible  order,  but  as 
a  system  which  sustains  the  greatest  resemblance  to  a 
planetary  system,  so  that,  just  as  in  the  latter  the  planets 
are  confined  very  nearly  to  a  common  plane,  so  also,  the 
fixed  stars  arrange  themselves  as  nearly  as  possible  in  their 
successive  zones,  upon  a  definite  plane  which  must  be  re- 
garded as  extended  through  the  whole  heaven,  and,  by 
means  of  their  densest  aggregation  in  such  plane,  trace 
out  that  luminous  belt  known  as  the  Milky  Way."f 

It  appears  that  Wright  entertained  the  conception  of 
other  firmamental  systems,  as  well  as  of  higher  orders  of 
systems  successively  ascending  until  the  entire  universe 
"revolved  about  the  throne  of  God,"  as  we  have  some- 
times found  the  thought  expressed  in  English  literature. 
Kant  refers  to  Wright  again  in  connection  with  the  ques- 
tion of  the  central  body  of  the  universe. \  "What  may 
be  the  constitution  of  this  fundamental  piece  of  the  entire 

*  Thomas  Wright:  An  Original  Theory,  or  New  Hypothesis  of  the  Universe, 
London,  1750,  4to.  An  American  edition,  with  Notes  by  Prof.  C.  8.  Rafinesque, 
was  published  in  8vo  at  Philadelphia  in  1837.  No  copy  exists,  however,  in  the 
library  of  \\te  Academy  of  Natural  Sciences  at  Philadelphia:  nor  have  I  been  able 
to  obtain  a  copy  of  the  work  in  any  edition. 

t  Kant's  Sfimmtliche  Werke,  i,  220. 

i  Kant's  Sammtliche  Werke.  i,  311. 


SPECULATIONS   OF   THOMAS   WRIGHT.  573 

creation,  and  what  may  be  found  upon  it,  we  leave  it  to 
Herr  Wright,  of  Durham,  to  'determine.  He,  with  fanati- 
cal enthusiasm,  elevated  in  this  happy  spot,  as  on  a  throne 
of  universal  nature,  a  powerful  being  of  the  divine  sort, 
possessed  of  spiritual  attractive  and  repulsive  powers,  who 
draws  to  himself  all  virtues  and  repels  all  vices  in  the 
boundless  sphere  through  which  his  activity  spreads." 

These  are  not  weighty  items  for  Kant  to  place  on  the 
credit  side  of  his  account  with  Wright;  and  it  would  ap- 
pear that  nebular  theory  is  still  less  indebted  than  Kant  to 
the  bold  English  speculator. 


CHAPTER  II. 

KANT'S    GENERAL    HISTORY    OF    NATURE. 

No  other  thinker  of  modern  times  has  been  throughout  his  work  so  pene- 
trated with  the  fundamental  conceptions  of  physical  science :  no  other  has  been 
able  to  hold  with  such  firmness  the  balance  between  empirical  and  speculative 
ideas. — Prof.  R.  ADAMSON. 

IMMANUEL  KANT  is  the  author  who  is  generally  re- 
garded the  first  to  outline  the  modern  cosmogonic 
theory  on  a  well  apprehended  basis  of  physical  principles. 
The  treatise*  in  which  his  views  are  set  forth  is,  in  many 
respects,  remarkable.  As  it  is  known  only  in  a  general, 
and  imperfect,  way,  to  a  large  majority  even  of  the  well 
informed,  I  shall  offer  a  somewhat  extended  digest  of  its 
positions.  It  will  be  noticed  that,  in  accordance  with  the 
spirit  and  usages  of  his  age,  he  entered  quite  freely  upon 
themes  which  a  strict  judgment  would  set  down  as  at  best 
only  collateral.  But  I  shall  endeavor  to  fairly  reproduce 
the  spirit  of  these  parts,  as  well  as  those  which  are  more 
strictly  scientific.  I  am  the  better  pleased  to  do  this  be- 
cause Kant  is  not  generally  credited  with  entertaining 
some  of  the  beliefs  which  are  clearly  reflected  in  the  theo- 
logical passages  of  this  work. 

§  1.    FIBMAMENTAL  ORGANIZATION. 

The  author  first  directs  attention  to  the  familiar  phe- 
nomena of  the  Milky  Way.  The  diffused  light  of  that 

*  Kant:  Allgeineine  Naturgeschichte  und  Theorie  des  Ittmtnelt,  oder  Versuch 
von  der  Verfassung  und  dem  mechanischen  Ursprunge  des  ganzen  Weltgebdudes, 
nach  Neicton'  schen  Grundsdtzen  abgehandelt.  Konigsberg  u.  Leipzig,  1755. 
Kant's  Sammtliche  Werke,  Hirteaatolo  edition,  Leipzig,  1867,  Bd.  i,  SS.  307-345. 


FIRMA MENTAL    ORGANIZATION.  575 

belt  he  attributes,  like  Herschel  after  him,  to  the  multi- 
tude of  stars  which  lie  in  the  line  of  vision;  and  the 
definiteness  of  the  belt  of  light  he  compares  to  the  "zo- 
diac" within  which  the  planets  of  our  solar  system  move. 
All  these  stars  he  conceives  to  be  travelling'  in  orbits  about 
the  centre  of  the  starry  system,  near  which  our  sun  is 
placed,  or,  perhaps,  around  more  than  one  centre.  These 
motions  secure  the  stability  of  the  system,  and  endow  it 
with  endless  perpetuity.  He  regards  the  comets  as  origi- 
nal members  of  the  solar  system,  and  their  high  inclina- 
tions and  erratic  movements  are  compared  with  the  more 
scattered  fixed  stars  which  lie  more  or  less  removed  from 
the  zone  of  the  Milky  Way.  Such  stars  he  calls  "the 
comets  among  the  suns."  But  why  are  not  these  move- 
ments among  the  stars  observed  by  astronomers?  He 
replies,  with  characteristic  sagacity,  that  their  immense 
distances  render  their  changes  of  position  imperceptible 
within  a  lifetime,  and  calculates  that  four  thousand  years 
would  be  required  for  one  of  the  nearest  to  move  over  an 
arc  of  one  degree.  But  he  anticipates  that  the  time  will 
come  when  these  movements  will  be  discovered.*  He 
remarks  that  the  ancients  noted  stars  in  definite  positions 
from  which  they  have  disappeared,  and  conjectures  that 
they  have  simply  changed  their  places.  The  excellence 
of  instruments  and  the  perfection  of  science  give  hope  of 
fixing  this  conjecture  on  a  certain  basis.  De  la  Hire  had 
already  remarked  decided  change  in  the  stars  of  the 
Pleiades. 

In  the  next  place  he  directs  attention  to  remarkable 
patches  of  light  now  known  as  nebulae.  Huygens  had 
regarded  them  as  openings  in  the  firmament  through 
which  the  glow  of  heaven  shone.  Maupertuis  had  consid- 

*  This  anticipation  has  been  f  ulfllled,  but  the  stellar  movements  do  not 
present  that  consentaneousness  required  by  Kant's  theory.  They  move  in  all 
directions,  and  not  alone  in  paths  parallel  with  the  plane  of  the  Miiky  Way. 
(See  pp.  140-1.) 


576         KANT'S  GENERAL  HISTORY  OF  NATURE. 

ered  them  heavenly  bodies  of  vast  dimensions.  But  Kant 
ventured  to  regard  them  as  remote  firmaments  of  stars 
whose  immense  distances  reduced  their  light  to  a  faint 
blended  luminosity.  To  him  they  were  only  other  Milky 
Ways,  with  motions  and  world  systems  akin  to  those  pre- 
sented by  our  firmament  and  solar  system. 

He  dwells  on  these  conceptions  with  warmth,  and  says: 
"They  open  to  us  an  outlook  upon  the  limitless  field  of 
creation,  and  afford  an  exhibition  of  the  work  of  God, 
which  is  commensurate  with  the  eternity  of  the  divine 
Worker."  *  *  *  "The  wisdom,  the  goodness,  the 
power  which  here  reveal  themselves  are  infinite,  and  in 
the  same  measure  productive  and  unresting;  the  plan  of 
their  revelation  must,  therefore,  be  precisely  like  them, 
infinite  and  boundless."* 

The  great  philosopher  falls  into  the  error  of  regarding 
the  comets  as  members  of  the  solar  system,  and  as  gener- 
ated by  the  same  mechanical  cause.  He  thinks  a  transi- 
tion may  be  discovered  between  the  planets  and  comets. 
The  eccentricities  of  the  planetary  orbits  increase,  as  a 
rule,  from  the  nearer  to  Saturn  —  the  remotest  known  in 
the  time  of  Kant.  The  exceptions  offered  by  Mercury  and 
Mars  may  be  attributed,  he  says,  to  their  smaller  mass,  by 
which  they  received  an  excess  of  the  centrifugal  influence. 
Is  it  too  much,  then,  to  anticipate  that  planets  which  we 
may  expect  to  discover  beyond  Saturn  will  possess  a  still 
higher  eccentricity,  and  thus  exhibit  a  graduation  toward 
the  class  of  cometary  bodies?  If  this  is  likely,  then  not 
alone  will  there  be  revealed  a  transition  toward  comets  in 
an  increasing  eccentricity  of  orbit,  and  thus  a  proof  that 
the  cause  which  imparted  to  both  their  orbital  motions 
became,  with  increase  of  distance,  feebler  and  less  able  to 
maintain  the  equilibrium  of  centripetal  and  centrifugal 
motions,  but  also  less  able  to  restrict  the  remoter  bodies 

*SSnuntlichc  Werke,  243. 


PLAXETOGENY.  577 

to  the  common  ecliptic  plane  which  the  comets  have  been 
permitted  so  singularly  to  abandon.  We  may,  therefore, 
expect  the  discovery  of  planets  beyond  Saturn,  whose 
eccentricity  will  diminish  the  gap  which  now  exists  be- 
tween planets  and  comets,  and  which  will  be  visible  only 
in  perihelion,  a  circumstance  which,  with  their  smaller 
dimensions  and  feebler  light,  has  hitherto  prevented  their 
discovery.  The  last  planet  and  the  first  comet  may  be 
regarded  the  same,  and  its  eccentricity,  we  may  believe, 
is  so  great  that  in  its  perihelion  it  intersects  the  orbit  of 
the  next  interior  planet  which,  perhaps,  is  Saturn  itself. 

§  2.     PLAKETOGENY. 

In  the  second  part  of  this  essay  Kant  approaches,  first, 
the  question  of  planetary  origins  and  the  causes  of  their 
motions.  In  contemplating  the  harmonious  movements  of 
the  planets,  two  considerations  impress  us:  First,  so 
extended  a  system  of  mutual  conformities  seems  to  dem- 
onstrate a  common  cause.  Second,  the  interplanetary 
spaces  are  so  vast  and  so  vacant  that  the  admission  of 
interacting  influences  seems  impossible.  Newton,  says 
he,  for  this  reason,  could  not  admit  the  existence  of  any 
material  cause  acting  across  the  intervals  of  the  planet- 
ary framework,  to  impress  common  movements.  He 
affirmed  that  the  immediate  hand  of  God  had  established 
the  observed  order  without  the  intervention  of  the  forces 
of  nature.  There  must,  however,  be  some  conception 
which  shall  unite  these  two  conflicting  principles  in  a  true 
system.  The  interplanetary  spaces  must  have  been  for- 
merly filled  with  a  supply  of  efficient  material  for  impress- 
ing the  uniform  motions  of  the  heavenly  bodies;  and  after 
gravitation  had  cleared  those  spaces,  and  all  disseminated 
material  had  been  gathered  in  separate  masses,  the  plan- 
ets must  continue  to  move  in  unresisting  space  with  the 
motion  impressed  upon  them.  I  assume,  he  says,  that  all 
37 


578         KANT'S  GENERAL  HISTORY  OF  NATURE. 

the  matter  of  the  solar  system,  in  the  beginning  of  all 
things,  existed  dissolved  into  its  elements,  and  filled  the 
entire  space  of  the  system.  Its  existence  is  an  outcome 
from  the  eternal  idea  of  the  Divine  Mind.  It  was  en- 
dowed with  a  tendency  to  form,  through  natural  develop- 
ment, a  more  perfect  constitution.  But  the  difference  in 
the  kinds  of  elements  induced  motion  in  nature,  and  an 
organization  of  the  fittest*  out  of  chaos;  so  that  the 
stagnation  which  must  have  resulted  from  universal  iden- 
tity of  material  was  disturbed,  and  the  chaos  began  to  be 
organized  at  the  points  of  the  more  powerfully  attracting 
particles.  These  drew  to  themselves  lighter  particles,  and 
the  larger  masses  attracted  the  smaller,  until  at  length  a 
collection  of  bodies  remained,  animated  by  motions  inher- 
ited from  the  past  conditions. 

But  nature  has  other  forces  in  store.  The  force  of 
repulsion  tends  to  the  dissolution  of  matter.  This  force, 
during  the  process  of  descent  of  particles  toward  the  cen- 
tre of  attraction,  developed  at  times  a  transverse  action, 
which  deviated  the  particle  from  a  direct  line,  and  inau- 
gurated a  tendency  to  rotary  motion.  Thus  came  into  ex- 
istence the  planetary  and  also  the  solar  motions. f  The 
beginning  of  planetary  formation, '  however,  is  not  to  be 
sought  alone  in  Newtonian  gravitation.  This  would  be 
too  slow  and  feeble.  We  should  rather  say  that  the  first 
organization  took  place  through  the  accumulation  of  sim- 
ple elements  united  by  the  customary  laws  of  cohesion, 
until  such  masses  were  formed  that  the  Newtonian  attrac- 
tion became  sufficient  to  continually  enlarg-e  them  by 
action  from  a  distance.  J 

Turning  next  to  the  densities  of  the  planets,  and  the 

*  "  Das  Vornehmste." 

t  Our  present  knowledge  of  the  invariability  of  the  total  quantity  of  motion 
within  a  system  exposes  a  fallacy  in  this  reasoning. 

iThis  is  another  m  sapprehension,  since  gravity  acts  upon  particles  as  well 
as  masses. 


PLANETOGENY.  579 

relations  of  their  masses,  it  is  apparent,  he  says,  that  the 
condensation  of  the  original  matter  must  be  proportioned 
to  the  distance  of  the  particles  from  the  attractive  centre. 
Newton  had  believed  that  the  variations  in  density  were 
produced  by  the  direct  will  of  God.  The  lightest  portions 
of  the  earth,  for  instance,  must  be  distributed  over  the 
surface.  Why  then  is  the  density  of  the  sun  less  than 
that  of  the  planets  ?  Because  the  planets  near  the  centre, 
and  in  fact  all  the  planets,  are  composed  of  particles  which, 
from  their  superior  density  have  been  drawn  toward  the 
centre,  displacing  the  lighter  particles  or  mingling  with 
them  in  more  than  the  normal  proportion,  while  on  the 
contrary,  the  body  at  the  centre  is  composed  of  the  gen- 
eral average  of  particles  in  respect  to  density,  among 
which  the  lighter  constitute  the  greater  part.*  In  accord- 
ance with  this  view,  concludes  the  author,  "  the  moon  is 
twice  as  dense  as  the  earth,  and  the  latter  four  times  as 
dense  as  the  sun ;  and  the  earth,  according  to  all  calcula- 
tion, will  be  surpassed  in  density  by  the  interior  planets 
Venus  and  Mercury."  f  The  increasing  ratio  of  planetary 
masses  as  we  recede  from  the  sun  is  connected  with  the 
increasing  diameters  of  the  spheres  of  attraction  of  the 
planets,  as  their  distances  diminish  severally  the  sun's  in- 
fluence. The  excessive  tenuity  of  the  original  stuff  is 
shown  by  the  fact  that  if  all  the  planets  were  reduced  to 
the  density  of  our  atmosphere,  their  matter  would  fill 

*The  passage  (Op.  cif.,  p.  256)  is  involved  and  obscure.  It  is  strange  that 
the  author  did  not  perceive  that  the  process  of  increasing  condensation  in  the 
dffused  mass  could  not  be  arrested  at  any  given  distance  from  the  centre,  but 
must  be  continued  quite  to  the  centre,  and  thus  render  the  central  body  the 
densest  of  all. 

t  Modern  astronomy  has  determined  the  following  densities  for  these  bodies : 
Sun,  .205;  Mercury,  1.21  (which  is  according  to  prediction) ;  Venus,  1.03;  Earth, 
1.00;  Moon,  .607.  Nevertheless,  the  remarkable  coincidence  remained,  as 
pointed  out  by  Buffon,  that  the  mean  density  of  all  the  planets  is  to  the  density 
of  the  sun  as  640  to  650.  But  finally,  the  mean  density  of  all  the  planets,  accord- 
ing to  present  knowledge,  and  allowing  for  differences  in  the  planetary  masses, 
is  to  the  density  of  the  sun  as  2%  to  255  or  as  640  to  552. 


580         KANT'S  GENERAL  HISTORY  OF  NATURE. 

fourteen  hundred  thousand  times  the  space  of  the  earth; 
while  this  is  thirty  million  times  less  than  the  entire  space 
which  the  matter  of  the  planets  is  supposed  to  have  filled 
originally. 

The  gradually  increasing  eccentricity  of  the  remoter 
planets  is  produced  by  the  diminished  centripetal  force  of 
the  solar  mass  upon  the  descending  particles,  and  their 
lower  density  and  hence  feebler  power  to  overcome  the 
resistance  offered  by  the  heavier  particles  to  their  direct 
descent  toward  the  sun.  These  conditions  attain  their 
maximum  in  the  region  of  the  comets  beyond  the  orbit  of 
Saturn.  To  them  are  due  also  the  high  inclinations  of  the 
cometary  orbits.  As  to  the  retrograde  motions  of  certain 
comets,  since  they  are  in  conflict  with  the  theory,  it  is 
conjectured  that  with  many  of  them  the  phenomenon  may 
be  only  an  optical  illusion. 

Satellites  have  come  into  existence  through  the  opera- 
tion, on  a  smaller  scale,  of  the  tendencies  recognized  in 
the  organization  of  the  planets.  Axial  rotations  have 
been  established  by  the  primitive  motions  of  the  gathering 
particles.  The  synchronism  of  the  moon's  axial  and 
orbital  motions  is  a  problem  left  for  future  solution.*  The 
moon's  rotation  was  probably  more  rapid  once  than  at 
present.  The  same  may  be  said  of  the  rotation  of  the 
earth.  The  inclinations  of  the  planetary  axes  may  have 
been  produced  by  an  excess  of  momentum  of  particles  de- 
scending upon  one  hemisphere;  but  more  probably,  pertur- 
bations have  intervened  to  disturb  the  original  positions 
of  the  axes.  Moreover,  the  uplift  of  mountain  masses 
unsymmetrically  disposed  must  tend  to  change  the  posi- 
tion and  inclination  of  the  axis  of  a  planet,f  though  this 

*This  seems  a  singular  statement,  since  the  author  had  already,  in  1754,  in  a 
prize  essay  presented  to  the  Academy  of  Sciences  in  Berlin,  ascribed  this  syn- 
chronism to  tidal  action  exerted  by  the  earth. 

•(•This  is  substantially  the  problem  discussed  by  Rev.  Samuel  Haughton 
(Proc.  Roy.  Soc.,  March  8, 1877,  xxvi,  51-5/55-63;  December  20,  1877,  xxvi,  534- 


PLANETOGENY.  581 

change  is  confined  within  limits.  Such  ore-graphic  dis- 
turbances belong1  to  the.  earlier  periods  of  planetary  life, 
and  Jupiter  seems  to  be  actually  undergoing  changes  inci- 
dent to  the  half-fluid  and  unsettled  condition.  "  In  such 
a  state  the  surface  can  experience  no  repose.  Upheavals 
and  ruin  reign  upon  it.  The  telescope  itself  assures  us 
of  this.  The  condition  of  this  planet  is  perpetually 
changing." 

The  author  next  considers  the  origin  of  the  rings  of 
Saturn.  A  planet  lying  at  the  distance  of  Saturn  must 
have  many  agreements  with  the  neighboring  comets,  if,  in 
fact,  it  has  entered  the  planetary  class  as  assumed,  through 
the  diminution  of  its  eccentricity.  Viewing  the  planet 
thus,  there  was  a  time  when  its  great  eccentricity  brought 
it,  in  perihelion,  into  close  proximity  with  the  sun.  The 
intense  solar  heat  lifted  its  lighter  material  from  the  sur- 
face in  the  form  of  vapor.  At  a  later  period,  with  a 
moderated  temperature,  the  vapors  assumed  the  form  of 
tails,  and  at  length  the  cometary  affinities  of  the  planet 
were  retained  only  in  the  permanent  ring  which  surrounds 
it.  In  short,  "Saturn  has  had  a  rotation  upon  its  axis, 
and  nothing  more  than  this  is  necessary."  *  *  *  "I 
venture  to  declare  that  in  all  nature  few  things  can  be  re- 
duced to  an  origin  so  intelligible."*  The  velocity  of  rota- 
tion of  the  ring  calculated  from  the  periodic  time  of  a 
satellite,  gives  the  velocity  of  the  equatorial  portion  of  the 
planet  at  the  time  of  the  separation  of  the  ring.  Thus 
the  planet's  rotation  is  found  to  be  6  h.  23  m.  53  sec.,  and 
he  leaves  it  for  the  future  to  test  the  result,  f 

Kant  had  knowledge  of  only  a  single  ring  around  Sat- 
urn. But  he  calculated  that  the  friction  of  outer  and 

46).  See,  also,  G.  H.Darwin's  criticism  (Proc.  Hoy.  Soc.,  March  14,  1878),  and 
Prof.  Haughton's  reply  (76.,  May  23, 1878). 

*  Op.  cit.,  275.  Here  is  a  distinct  enunciation  of  the  principle  of  annulation 
afterward  employed  by  Laplace. 

tit  is  given  in  recent  works  as  10  h.  14  m. 


582         KA.NT'S  GEXERAL  HISTORY  OP  MATURE. 

inner  parts,  due  to  difference  of  velocity  must  tend  to  the 
destruction  of  the  ring.  Instead  of  this  event,  however, 
it  would  separate  into  several  concentric  rings,  each  re- 
volving in  its  own  period.*  The  number  of  these  rings 
could  be  computed  if  the  degree  of  connection  between 
the  constituent  particles  were  known.  In  any  event,  the 
equilibrium  and  stability  of  the  rings  is  provided  for.  As 
to  the  condition  of  the  matter  of  the  rings,  Kant  continu- 
ally speaks  of  particles  and  small  parts  {Thettchen),  and 
clearly  conveys  the  identical  conception  which  has  been 
enunciated  by  Peirce  and  Clerk-Maxwell  in  recent  times. 
In  a  note  of  later  date,  he  cites  with  satisfaction  a  record 
made  by  Cassini  \  half  a  century  before,  in  which  the  con- 
jecture is  offered  that  "perhaps  this  ring  may  be  a  sicarm 
of  small  satellites,  which  to  an  observer  from  Saturn  may 
present  somewhat  the  aspect  of  the  Milky  Way  from  the 
earth."  Kant  also  cites  with  satisfaction  the  confirmation 
already  furnished  by  Cassini,  of  his  argument  for  the  ex- 
istence of  several  rings.  He  takes  great  pleasure,  he  says, 
in  offering  his  theory  of  the  rings,  since  he  has  the  hope 
that  it  may  be  confirmed  by  new  observations  to  be  made 
with  the  improved  telescope  which  he  hears  that  Bradley 
has  had  placed  at  his  disposal. 

As  to  the  possibility  of  rings  about  other  planets,  he 
shows  by  a  simple  calculation,  based  on  the  diameter  of 
Jupiter,  its  period  of  rotation  and  the  attractive  force 
upon  its  surface,  that  a  Jovian  ring  is  impossible  under 
present  relations  of  these  factors.  He  shows  the  same 
in  reference  to  the  earth.  J  But  in  former  times,  when  the 

'Compare  the  alleged  tendency  to  stratification,  stated  on  p.  119. 

t Memolres  Acad.  Sci.,  Paris,  1705. 

Jin  an  editorial  note  ia  given  the  substance  of  an  oral  statement  made  by 
Kant  concerning  his  theory  in  1791.  He  thinks  it  has  received  much  confirma- 
tion, especially  through  the  light  thrown  upon  it  by  a  "Supplement "  published 
by  Herr  Hofrath  Lichtenbcrg,  who  suggests  that  in  any  aeriform  "Urstoff" 
disseminated  through  space  a  high  degree  of  elasticity  must  subsist,  until 
through  gravitational  pressure  it  should  be  destroyed;  after  which  the  density 


THE  COSMOS  IN"  ITS  TOTALITY.  583 

axial  rotation  of  the  earth  was  much  more  rapid,  a  ring 
may  have  existed.  "What  beauty  of  aspect  for  those  who 
were  created  to  inhabit  the  earth  as  a  Paradise !  How 
great  a  convenience  for  those  on  whom  nature  smiled  from 
every  side  ! "  This  ring  must  have  consisted  of  watery 
vapor.  Why  may  not  its  disruption  through  contact  with 
a  misdirected  comet,  or  the  process  of  cooling  and  con- 
densation, have  precipitated  upon  the  earth  that  destruc- 
tive flood,  the  Mosaic  narrative  of  which  has  so  puzzled  all 
commentators  ?  * 

In  this  connection  the  Zodiacal  Light  is  conjecturally 
referred  to  the  same  explanation  as  the  Saturnian  ring. 
It  is  regarded  as  a  ring  of  particles  surrounding  the  sun,f 
and  lying  nearly  in  the  plane  of  his  equator. 

§  3.  THE  COSMOS  IN  ITS  TOTALITY. 

The  author  proceeds  now,  in  the  seventh  chapter  of 
the  Second  Part,  to  a  more  particular  consideration  of  the 
infinitude  of  the  creation  at  large,  both  in  respect  to  space 
and  time.  "  The  cosmical  fabric,  through  its  immeasur- 
able magnitude  and  the  endless  variety  and  beauty  which 
shine  forth  from  it  on  all  sides,  impresses  us  with  silent 
amazement."  This  feeling  is  enhanced  by  the  discovery 
that  this  vast  array  of  phenomena  flows  from  the  orderly 
and  eternal  working  of  a  single  general  law.  The  stars 
are  centres  of  other  systems  like  our  own.  They  are  com- 
posed of  the  same  elementary  particles.  Like  the  planets 
of  our  zodiac,  they  are  arranged  in  a  limited  zone  which 
we  style  the  Milky  Way.  "  The  Milky  Way  is  the  zodiac 

would  become  so  increased  that  great  heat  would  be  developed  which,  in  the 
larger  bodies  like  the  sun,  would  be  accompanied  by  luminosity,  but  in  the 
smaller,  like  the  planets,  would  produce  only  an  internal  heat.  Here  is  the  con- 
tractional  theory  in  the  bud. 

*This  recalls  William  Winston's  grave  conjecture  that  the  Flood  was  caused 
by  a  blow  from  the  tail  of  a  comet. 

t  Poetically  styled  the  "  Halsschmuck  der  Sonne."  This  is  precisely  the 
modern  view. 


584         KANT'S  GENERAL  HISTORY  OF  NATURE. 

of  the  higher  world  orders."  But  even  beyond  the 
bounds  of  the  system  of  the  Milky  Way,  are  other 
firmamental  systems  —  other  Milky  Ways.  We  contem- 
plate with  amazement  their  faint  figures  pictured  on  the 
concave  vault  of  heaven.  The  worlds  of  all  these  sys- 
tems, to  insure  their  stability,  must  necessarily  possess 
motions  analogous  to  those  of  our  own  system.*  But  has 
the  succession  of  ever  ascending  world  systems  no  end  ? 
It  would  be  preposterous  to  contemplate  the  minute  por- 
tion of  space  which  we  survey  as  the  limit  of  the  field  of 
the  divine  activities.  It  is  more  suitable,  more  necessary 
to  conceive  the  realm  of  the  material  creation  as  abso- 
lutely without  bounds.  We  have  good  ground  to  con- 
clude that  the  store  of  created  matter  f  suffices  for  the 
production  of  a  chain  of  cosmical  order  without  limit. 
The  basis  matter  itself  is  an  immediate  consequence  of 
the  divine  existence,  and  must  necessarily  be  so  exhaust- 
less  and  enduring  as  to  extend  the  development  of  material 
organization  over  a  plan  of  creation  embracing  all  exis- 
tence possible,  without  measure  and  without  end.  One 
might  well  conceive  an  endless  succession  of  mutually 
disconnected  world  systems  ;  but  such  a  plan  would  not 
provide  for  the  perpetuity  of  order  ;  and  unless  the 
common  principle  of  attraction  extended  through  the  en- 
tire universe  of  matter,  there  would  be  wanting  that  char- 
acter of  persistence  which  is  the  mark  of  the  choice  of 
God. \  But  a  universal  coordinating  principle  implies  one 
common  centre,  and  one  vast  central  mass  of  matter. 
Here  the  process  of  creation  began.  From  this  middle 
point  it  has  extended  continually  outward  over  the  infi- 
nite chaotic  waste  of  unorganized  material  atoms.  I 

*In  this  connection  he  nses  the  expression,  Dag  Llcht  welches  nut-  eine 
tinyedruckte  Bewegung  M,  which  is  equivalent  to  the  intimation  that  light  ia 
only  "  a  mode  of  motion." 

t  Der  Vorrath  des  erschaffenen  Naturstoffes. 

$Die  Bfstandigkeit  die  das  Merkmal  dtr  Wohl  Gottes  ist. 


\ 
THE   COSMOS   IN   ITS  TOTALITY.  585 

know  of  nothing  which  can  lift  the  soul  of  man  to  a 
nobler  amazement  than  the  outlook  over  this  boundless 
field  of  Almighty  power.  Worlds  rise  into  being  upon 
worlds,  in  endless  progress  ;  and  beyond  the  outer  bounds 
of  the  widest  realm  of  order,  confusion  and  chaos  forever 
contend  on  a  field  as  limitless  as  if  the  work  of  creation 
had  not  already  attained  an  endless  development.  Assign 
what  diameter  we  will  to  the  completed  creation,  we  are 
always  near  the  middle  point ;  beyond  the  periphery  of 
the  sphere,  over  the  infinite  expanse,  lie  buried  in  the 
stillness  of  night,  the  germs  of  order  awaiting  the  pro- 
gress of  eternity  to  be  quickened  into  active  life.  So  the 
process  of  cosmical  organization  extends  itself.  "Crea- 
tion is  not  the  work  of  a  moment."  Millions  and  moun- 
tain ranges  of  millions  of  ages  will  flow  away  arid  "the 
creation  will  never  be  complete.  It  was  indeed  once  be- 
gun, but  it  will  never  end." 

It  is  perhaps  a  daring  conjecture  that  the  cosmic  pro- 
ductiveness of  one  part  of  immensity  implies  the  com- 
parative exhaustion  of  another  part.  But  the  resources 
of  the  universe  are  never  diminished,  for  they  are  nothing 
else  than  the  exercise  of  the  divine  omnipotence  itself. 
The  decay  of  worlds  is  but  a  part  of  the  universal  order 
which  brings  plants  and  animals  and  man  himself  to  de- 
struction, only  to  be  succeeded  by  new  organisms  at  some 
other  point.  "  Whatever  has  origin  and  beginning  has  in 
itself  the  characteristic  of  its  finite  nature  ;  it  must  decay 
and  come  to  an  end."  As  man  in  course  of  time,  retires 
from  the  stage  on  which  he  has  acted  his  part,  so  worlds 
and  systems,  when  their  role  is  played,  vanish  from  the 
scene.  The  infinitude  of  creation  is  wide  enough  to  spare 
a  world  or  a  Milky  Way  as  easily  as  a  flower  or  an  insect. 
"  Meanwhile  eternity  is  adorned  with  ever  varying  mani- 
festations, because  God  remains  active  in  the  unceasing 
work  of  creation." 


586         KANT'S  GENERAL  HISTORY  OF  NATURE. 

But  when  a  system  of  worlds  has  fallen  into  disorder 
and  decay,  will  no  power  be  extended  to  effect  a  reorgan- 
ization ?  We  cannot  long  remain  in  doubt  when  we 
reflect  that  the  ceaseless  exhaustion  of  the  motions  of  the 
planetary  system  must  finally  precipitate  planets  and 
comets  together  upon  the  body  of  the  sun,  and  that  then 
the  solar  heat  must  undergo  an  increase  so  immeasurable 
as  to  dissipate  again  the  particles  of  the  common  mass 
through  the  distant  regions  of  space  from  which  they  had 
been  originally  gathered  together.  Then  must  begin 
again  the  process  of  world  organization  whose  completed 
cycle  has  been  traced. 

As  a  planetary  system  seems  destined  to  decay,  so  the 
hosts  of  the  system  of  the  Milky  Way  must  be  conceived 
as  wasting  inevitably  the  forces  by  which  they  are  ani- 
mated. Countless  suns  will  be  precipitated  upon  the 
mighty  central  mass;  but  the  tremendous  shock  will  kindle 
an  unimaginable  intensity  of  glow,  which  must  dissolve 
the  bonds  of  matter,  and  expel  its  ultimate  constituents 
again  throughout  the  vast  limits  before  engirt  with  the 
fiery  girdle  of  the  firmament.  The  soul  of  man  in  think- 
ing of  events  of  such  stupendous  magnitude  sinks  within 
him  in  deepest  amazement.  But  the  vastness  of  objects 
and  events  so  enstamped  with  the  characters  of  change 
and  mutability  leaves  the  soul  still  unsatisfied;  "it  feels  a 
desire  to  know  more  intimately  that  Being  whose  intelli- 
gence, whose  greatness,  is  the  fountain  of  that  light  which, 
as  if  from  a  central  source,  illuminates  the  totality  of 
nature."  "Happy  soul  if  amid  the  tumult  of  the  elements 
and  the  ruin  of  nature,  it  can  look  down  always  from  its 
lofty  position,  and  see  the  current  of  desolation  which 
brings  ruin  to  all  finite  things  sweep  by,  as  it  were,  be- 
neath its  feet."  "When,  then,  the  fetters  which  hold  us 
bound  to  the  vanity  of  created  existence,  in  the  moment 
appointed  for  the  transformation  of  our  being  shall  have 


OUR   SUN  AND   OTHER   SUNS.  587 

fallen  off,  then  will  the  undying  spirit,  freed  from  depend- 
ence on  finite  things,  find  the  enjoyment  of  true  happi- 
ness in  communion  with  the  eternal  existence." 

§  4.  OUR  SUN  AND  OTHER  SUNS. 

The  more  particular  constitution  and  activities  of  the 
sun  result  from  the  nature  of  the  primitive  particles  and 
their  mode  of  condensation.  The  lightest  parts  of  the  com- 
mon matter  which  moves  in  the  interplanetary  spaces,  from 
lack  of  adequate  momentum  are  overcome  by  centripetal 
force  and  precipitated  on  the  central  body.  But  these 
parts  are  also  the  most  energetic  in  the  production  of  fire; 
and  thus  we  see  that  through  their  addition  to  the  central 
body  it  becomes  a  flaming  orb.  "  On  the  contrary,  the 
heavier  and  inefficient  material,  and  the  lack  of  fire-pro- 
ducing particles  make  of  the  planets  only  cold  and  dead 
clumps  deprived  of  such  a  property."  The  sun  must  be 
surrounded  by  an  atmosphere.  "  Without  atmosphere  no 
fire  burns."  Now,  considering  the  great  mass  of  the  sun, 
to  what  a  density  must  this  atmosphere  attain,  and  what 
intensity  of  combustion  must  it  support.  In  this  atmos- 
phere ascend  clouds  of  smoke  consisting  of  commingled 
grosser  and  finer  particles  which,  cooled  in  the  higher 
regions,  precipitate  a  rain  of  pitch  and  sulphur  which 
afford  the  flames  new  aliment.  This  atmosphere,  too,  like 
that  of  the  earth,  is  beaten  by  winds,  and  we  may  well 
imagine  to  what  violence  they  must  attain.  But  as  is 
manifest,  all  flame  devours  its  atmosphere,  and  without 
doubt  the  solar  atmosphere  must  undergo  a  slow  exhaus- 
tion. It  is  true,  the  interactions  of  the  elements  tend  to 
replenish  the  atmosphere,  that  vast  supplies  must,  for  a 
long  time,  burst  forth  from  concealed  caverns  in  the  solar 
structure,  and  that  many  substances,  like  saltpetre,  are 
exceedingly  productive  of  elastic  gases,  yet,  though  such 
causes  must  greatly  prolong  the  solar  heat,  it  must  be 


588         KANT'S  GENERAL  HISTORY  OF  NATURE. 

admitted  the  sun  is  in  real  danger  of  final  extinction.  The 
central  body  of  our  system  will  be  quenched  in  eternal 
darkness.  Undoubtedly,  in  the  progress  of  decay,  new- 
found material  may  sustain  an  occasional  outburst  of  fiery 
energy,  as  with  other  suns  in  our  firmament,  which  have 
been  seen  to  assume  a  sudden  luminosity  and  then  to  wane, 
yet  our  central  orb  must  finally  attain  the  exhausted  and 
defunct  condition  which  awaits  all  finite  organizations. 
But  its  dead  substance  disseminated  through  space  will 
plant  chaos  with  the  germs  of  new  worlds. 

"Let  us  contemplate  in  imagination,  from  a  nearer 
standpoint,  an  object  so  extraordinary  as  a  burning  sun. 
At  a  glance  we  behold  oceans  of  fire  which  raise  their 
flames  to  heaven;  raging  storms  of  most  fearful  intensity 
which  rolling  over  the  shores  submerge  at  times  the 
elevated  regions  of  the  orb,  and  at  times  sink  back  upon 
their  borders;  burned-out  rocks  which  from  their  flaming 
throats  project  their  frightful  tongues  of  fire,  and  whose 
submergence  and  emergence  by  the  fluctuating  fiery  ele- 
ments is  the  cause  of  the  appearance  and  disappearance  of 
the  solar  spots;  dense  vapors  which  choke  the  fire,  and 
which,  uplifted  by  the  force  of  the  wind,  condense  in  dark 
clouds  which  storm  down  again  in  torrents  of  fiery  rain, 
and  as  burning  streams  descending  from  the  heights  of  the 
solid  land,  pour  themselves  into  the  flaming  valleys,  the 
crash  of  the  elements,  the  refuse  of  burned-out  matter  and 
the  disintegration  of  exhausted  nature  which  through  this 
terrible  stage  of  desolation  itself  works  out  the  beauty  of 
the  world  and  the  uses  of  the  created  being."  * 

If  all  the  stars  are  flaming  suns,  still  more  must  the 

*  Op,  cit.,  309-10.  In  connection  with  the  supposed  "  solid  land  "  of  the 
sun,  the  author  observe?,  in  a  note,  that  the  formation  of  a  world  from  material 
in  a  fluid  state  necessitates  the  development  of  inequalities  of  surface.  After  a 
crust  begins  to  form,  the  confined  gases  would  uplift  it  in  places  and  accumulate 
in  immense  caverns,  producing  on  the  surface  alternating  elevations  and 
valleys.  This  is  an  echo  of  Leibnitz. 


THE  MECHANICAL  CONSTITUTION  OF  THE  WOELD.    589 

central  body  of  the  Milky  Way  be  such.  Why  then  does 
it  not  become  visible  ?  The  answer  is  obvious,  when 
we  consider  that  if  that  body  were  ten  thousand  times 
the  bulk  of  our  sun,  and*  removed  a  hundred  ^mes  as  far 
as  Sirius,  it  would  appear  no  larger  than  that  star. 
Future  times  may  discover  it,  or  at  least  the  region  in 
which  it  is  located.  I  venture  the  conjecture  that  Sirius 
himself  is  the  central  body  of  the  Milky  Way.  What 
may  be  the  nature  and  condition  of  the  central  mass  of 
the  universe  is  a  problem  which,  perhaps,  involves  us  in 
rasher  conjecture  than  a  scientific  theory  allows;  but  I 
cannot  admit  with  Wright  that  here  the  person  of  the 
Godhead  is  specially  present.  The  divine  presence  is 
essentially  and  equally  in  every  domain  and  place.  I  im- 
agine, on  the  contrary,  that  the  higher  ranks  of  rational 
beings  belong  in  regions  remote  from  the  universal  centre. 
The  density  of  the  more  central  matter,  whatever  rela- 
tions subsist  between  matter  and  spirit,  must  necessarily 
impart  a  greater  degree  of  sluggishness  and  dulness  to 
more  central  intelligences,  while  a  keener  insight  and 
deeper  penetration  should  characterize  spiritual  life  con- 
nected with  the  lighter  matter  which  pervades  the  region 
of  more  freshly  organized  cosmical  existence. 

§  5.     THE  MECHANICAL  CONSTITUTION  OF  THE  WORLD. 

The  eighth  chapter  of  the  Second  Part  of  the  work 
offers  some  general  reflections  on  the  mechanical  constitu- 
tion of  the  world,  and  the  inferences  which  may  be  legiti- 
mately deduced.  "It  is  impossible,"  the  author  says,  "to 
contemplate  the  fabric  of  the  world  without  recognizing 
the  admirable  order  of  its  arrangement,  and  the  certain 
manifestation  of  the  hand  of  God  in  the  perfection  of  its 
correlations.  Reason,  when  once  it  has  considered  and 
admired  so  much  beauty  and  so  much  perfection,  feels  a 
just  indignation  at  the  dauntless  folly  which  dares  ascribe 


590         KANT'S  GENERAL  HISTOKY  OF  NATUEE. 

all  this  to  chance  and  a  happy  accident.  It  must  be  that 
the  highest  wisdom  conceived  the  plan,  and  infinite  power 
carried  it  into  execution."  He  proceeds  to  defend  the 
mechanical0theory  of  the  universe  against  the  charge  of 
"  naturalism/'  and  maintains  that  "  the  procedure  of  those 
naturalists  who  have  delivered  themselves  of  that  kind  of 
world  wisdom  must  make  solemn  apologies  at  the  bar  of 
religion."  One  of  the  characteristic  passages  from  this 
discussion  is  the  following  conclusion:  "Nature,  its  gen- 
eral properties  aside,  is  productive  only  of  beautiful  and 
perfect  fruits,  which  display  not  alone  harmony  and  per- 
fection, but  also  harmonize  perfectly  with  the  whole  com- 
pass of  nature,  with  the  needs  of  man  and  the  honor  of 
the  divine  attributes.  It  hence  follows  that  nature's  prop- 
erties can  possess  no  independent  necessity,  but  that  they 
must  have  their  origin  in  a  single  Understanding  as  the 
ground  and  source  of  all  being,  in  which  they  have  been 
ordained  in  accordance  with  universal  relations.  All 
things  which  set  forth  reciprocal  harmonies  in  nature 
must  be  bound  together  in  a  single  existence  on  which 
they  collectively  depend.  Thus  there  exists  a  Being  of 
all  beings,  an  infinite  Understanding  and  a  self-existent 
Wisdom,  from  which  nature,  in  the  whole  aggregate  of 
her  correlations,  derives  existence.  Further,  it  is  not 
allowable  to  maintain  that  the  activity  of  nature  is  preju- 
dicial to  the  existence  of  a  highest  Being;  the  more  per- 
fect it  is  in  its  developments,  the  better  its  general  laws 
contribute  to  order  and  harmony,  the  more  conclusive  is 
the  demonstration  of  the  Godhead  from  whom  these  rela- 
tions are  borrowed.  His  productiveness  is  no  longer  the 
operation  of  chance,  or  the  consequence  of  accident;  from 
him  flows  everything  according  to  unalterable  laws,  which, 
therefore,  must  produce  only  what  is  fit,  because  they  are 
only  the  reflection  of  a  scheme  infinitely  wise,  from  which 
all  disorder  is  banished.  It  is  not  the  fortuitous  con- 


DEDUCTIONS   TOUCHING    HABITABILITY,  ETC.        591 

course  of  the  atoms  of  Lucretius  which  has  builded  the 
world;  implanted  forces  and  laws  whose  source  is  the 
wisest  Understanding,  have  been  the  unvarying  cause  of 
that  order  which  can  only  flow  from  them,  not  by  chance 
but  by  ordination."* 

The  author  repeats  the  enumeration  of  the  mechanical 
relations  of  the  solar  system,  and  maintains  at  length  the 
improbability  and  unreasonableness  of  the  view  which 
ascribes  them  all  to  the  immediate  hand  of  God.  Never- 
theless, he  says:  "We  rightly  believe  that  fit  arrange- 
ments, which  tend  toward  a  useful  end.  must  have  a  wise 
understanding  for  their  originator;  and  we  are  perfectly 
at  liberty  to  think,  if  we  choose,  that  since  the  natures  of 
things  recognize  no  other  origin,  their  present  and  uni- 
versal constitution  must  have  a  natural  tendency  to  fit 
and  mutually  harmonious  consequences."  We  need  not 
hesitate  to  admit  the  operation  of  mechanical  causes  in 
nature,  "since  whatever  proceeds  from  them  is  not  the 
working  of  blind  fate  or  irrational  necessity,  but  is 
grounded  finally  in  the  highest  wisdom,  from  which  the 
constitution  of  nature  borrows  all  its  harmonies.  This 
conclusion  is  perfectly  correct:  If  in  the  constitution  of 
the  world  order  and  beauty  appear,  then  a  Deity  exists. 
But  the  other  decision  has  not  less  foundation:  If  this 
order  has  proceeded  from  the  general  laws  of  nature,  then 
all  nature  is  necessarily  a  working  of  the  highest  wisdom. "f 

§  6.  DEDUCTIONS  TOUCHING  HABITABILITY  AND  UNITY 
IN  THE  SYSTEM  OP  WORLDS. 

The  Third  Part  of  the  treatise  is  devoted  to  a  research 
concerning  the  influence  which  must  be  exerted  on  the 
spiritual  natures  of  the  different  planetary  inhabitants  by 
the  nature  of  the  matter  of  which  their  bodies  must  be 
constituted.  An  unquestionable  and  intimate  interaction 

*  Op.  cit.,  315-6.  t  Op.  cit.,  337. 


592         KANT'S  GENERAL  HISTORY  OF  NATURE. 

exists  between  mind  and  body.  The  original  constitution 
and  the  casual  conditions  of  the  body  control,  to  a  large 
extent,  the  operations  of  the  spiritual  faculties.  Since, 
therefore,  the  planets  near  the  sun  are  composed  of  heavier 
and  more  sluggish  matter  than  the  remoter  planets,  it  must 
be  that  their  inhabitants  are  endowed  with  less  mental 
agility  and  a  feebler  power  for  thought  and  imagination. 
Jupiter  seems  indeed  to  exist  in  that  formative  condition 
which  naturally  precedes  the  reception  of  organic  popula- 
tions, but  if  his  habitability  is  supposable,  it  seems  strongly 
probable  that  his  rational  occupants,  as  well  as  lower  ani- 
mals and  plants  are  formed  of  such  light  and  active  ma- 
terial elements  as  give  an  easier  and  more  rapid  activity  to 
the  discharge  of  their  organic  functions.  The  same  may, 
with  still  greater  probability,  be  conjectured  of  Saturn. 
As  the  mind  is  correlated  to  the  body,  the  rational  natures 
of  these  distant  populations  must  exceed  our  own  corre- 
spondingly, in  expertness  and  comprehension.  As  all  our 
apprehensions  of  external  things  are  measured  by  the  im- 
pression made  by  the  universe  upon  the  susceptibility  of 
our  material  faculties  of  cognition,  it  may  well  be  imagined 
that  the  remoter  populations  of  our  system  have  attained 
to  knowledge  which  stretches  hopelessly  beyond  the  reach 
of  terrestrial  intelligences. 

All  material  existence,  however,  is  bound  together  in 
the  common  rational  unity  which  finds  its  origin  in  the 
infinite  Mind;  and  since  even  terrestrial  intelligence  is 
gifted  with  the  power  to  seize  hold  on  the  chain  of  inter- 
connection, it  discovers,  though  perhaps  faintly,  the  reve- 
lations of  the  divine  perfections  which  nature  displays  to 
all  rational  beings.  Man,  perhaps,  stands,  in  the  ranks  of 
created  beings,  between  those  who,  on  the  one  hand,  are 
too  pure  to  sin,  and  those,  on  the  other,  who  are  too  un- 
intelligent to  sin.  Man,  perhaps,  partakes  exceptionally 
of  the  power  to  feel  simultaneously  the  temptation  to  sin 


SYNOPSIS   OF    POINTS    IN   THE   THEORY   OF    KAXT.    593 

and  the  aspiration  to  purity;  but  he  feels  that  his  immor- 
tal soul,  gifted  with  being  which  even  death  cannot  end, 
but  can  only  change,  is  destined  to  an  eternity  of  life  un- 
confined  to  a  single  planet,  but  privileged  to  seek  and  at- 
tain the  loftiest  knowledge  revealed  in  all  the  departments 
of  the  domain  of  Omniscience.  This  remarkable  treatise 
concludes  with  the  following  paragraph: 

"When,  indeed,  one's  soul  has  been  filled  with  contemplations 
like  these,  the  view  of  the  starry  heavens  on  a  cloudless  night,  con- 
fers a  species  of  delight  which  only  a  noble  susceptibility  can  appre- 
ciate. In  the  general  stillness  of  nature  and  composure  of  thought, 
the  mysterious  intuitions  of  the  undying  spirit  speak  an  unutterable 
language,  and  yield  unfonnulated  conceptions  which  it  feels,  indeed, 
but  can  never  describe.  If  among  the  thinking  creatures  of  this 
planet,  beings  exist  so  degraded  that  in  the  presence  of  all  the  in- 
ducements with  which  our  exalted  position  invites  them,  they  still 
hold  themselves  fast  bound  in  the  service  of  vanity,  Jiow  ill-starred 
is  this  globe  that  it  could  nourish  creatures  so  wretched!  But  how 
fortunate  is  it,  on  the  other  hand,  that  among  all  the  most  desirable 
conditions  possible,  a  way  is  opened  to  attain  bliss  and  exaltation 
which  rise  infinitely  above  all  the  preeminence  conferred  by  the  most 
advantageous  organization  of  nature  upon  any  one  of  the  heavenly 
bodies." 

§  7.   SYNOPSIS  OP  POINTS  IN  THE  COSMOGONIC  THEORY 
OF  KANT. 

1.  Points  correctly  taken,  according  to  more,  recent 
opinion. 

(1.)  The  diffused  galactic  light  results  from  the  multi- 
tude of  stars  lying  in  the  direction  of  the  galaxy. 

(2.)  The  stars  must  all  be  in  motion,  but  their  great 
distances  demand  thousands  of  years  to  render  their  mo- 
tions clearly  apparent.  Future  observation  will  demon- 
strate these  motions. 

(3.)  The  nebulas  are  other  firmaments.  Though  this 
opinion  was  entertained  by  the  elder  Herschel  respecting 
resolvable  nebulas,  recent  opinion  can  hardly  be  said  to  be 


594         KANT'S  GENERAL  HISTORY  OF  NATURE. 

formed  concerning  them;  but  of  irresolvable  nebula?  it  de- 
nies the  conclusion  of  Kant. 

(4.)  The  interplanetary  spaces  must  have  been  filled 
formerly  with  a  supply  of  matter.  All  the  matter  of  our 
system  was  formerly  dissolved,  and  filled  the  entire  space. 
Its  tenuity  was  excessive. 

(5.)  Aggregation  and  organization  began  around  cer- 
tain centres  of  attraction. 

(6.)  The  densities  of  the  planets  should  diminish  from 
the  centre  outward. 

(7.)  The  greater  masses  of  the  exterior  planets  depend 
on  the  diminished  power  of  the  solar  attraction  in  the 
remoter  parts  of  the  primitive  stuff. 

(8.)  The  synchronistic  motions  of  the  moon  are  due  to 
ancient  geal  tides  on  that  satellite.  The  solar  and  lunar 
tides  are  correspondingly  diminishing  the  earth's  rotary 
velocity. 

(9.)  The  axial  inclinations  of  the  planets  are  probably 
due  to  perturbations. 

(10.)  The  uplift  of  mountain  axes  must  affect  the  posi- 
tion of  the  axis  of  rotation  of  a  planet. 

(11.)  Jupiter  exists  in  a  half  fluid  and  formative  con- 
dition, not  yet  fitted  for  habitation. 

(12.)  The  ring-condition  results  from  axial  rotation  of 
incoherent  matter. 

(13.)  Unequal  velocities  of  outer  and  inner  zones  of 
a  nebulous  ring  would  result  in  separation  into  two  or 
more  rings.  The  ring  of  Saturn  is  probably  multiple. 

(14.)  The  Saturnian  ring  is  a  swarm  of  discrete  par- 
ticles or  minute  satellites. 

(15.)  Jupiter  and  the  earth  do  not  present,  in  our 
day,  the  physical  conditions  required  for  the  existence 
of  rings. 

(1C.)  At  a  former  period,  when  the  rotation  was  much 
more  rapid,  the  earth  may  have  had  a  ring  of  watery  vapor. 


SYNOPSIS   OF    POINTS   IN  THE  THEORY   OF   KANT.  595 

(17.)  The  zodiacal  light  is  a  ring  of  particles  surround- 
ing the  sun. 

(18.)  The  fixed  stars  are  centres  of  other  systems  com- 
posed of  the  same  substances  as  our  sun. 

(19.)   Light  is  only  a  motion  impressed. 

(20.)  The  process  of  world  making  is  continuous.  The 
decay  of  worlds  is  but  part  of  the  universal  order  which 
returns  in  new  worlds. 

(21.)  Whatever  begins  is  finite  and  must  come  to  an 
end. 

(22.)  Planets  and  comets  must  finally  be  precipitated 
upon  the  body  of  the  sun  ;  and  the  impact  must  generate 
enormous  heat. 

(23.)  Similarly,  the  present  order  which  pervades  the 
starry  system  must  come  to  an  end. 

(24.)   The  heat  of  the  sun  is  destined  to  extinction. 

(25.)  Extremely  violent  actions  are  taking  place  upon 
the  solar  surface,  and  the  solar  flames  rise  to  heaven. 

(26.)  The  inhabitants  of  all  worlds  are  bound  together 
by  a  common  rational  apprehension  of  the  system  of 
nature. 

2.    Points  considered  incorrectly  taken. 

(1.)  The  fixed  stars  all  move  in  orbits  about  a  common 
centre. 

(2.)  The  comets  are  original  members  of  the  solar 
system. 

(3.)  The  eccentricities  of  the  planetary  orbits  will  be 
found  to  increase  from  the  centre  to  the  periphery  of  the 
system. 

(4.)  Rotary  motions  resulted  from  repulsive  action  ex- 
erted from  centres  of  matter  on  descending  particles. 

(5.)  The  incipiency  of  aggregation  resulted  from  co- 
hesions rather  than  from  Newtonian  attraction. 

(6.)  The  ring  of  Saturn  results  from  intense  solar  heat 
exerted  during  perihelion,  at  a  period  when  Saturn's  ec- 


596         KANT'S  GENERAL  HISTORY  OF  NATURE. 

centricity  was  very  great.  It  is  a  transformed  cometary 
tail. 

(7.)  The  precipitation  of  planets  and  comets  upon  the 
sun  would  create  sufficient  heat  to  dissipate  the  matter  of 
the  system  and  reinaugurate  the  process  of  planetary 
evolution. 

(8.)  Mountainous  inequalities  in  the  crust  of  a  solidi- 
fying world  would 'result  from  the  action  of  confined 


(9.)    There  must  be  a  central  body  for  the  revolutions  of 
the  Milky  Way  ;  and  this  probably  is  Sirius. 


CHAPTER  III. 

DR.  LAMBERT  AND   SIR   WILLIAM   HERSCHEL. 

§  1.  LAMBERT'S  COSMOLOGICAL  LETTERS.* 

"T  AMBERT'S  work  was  written  in  popular  style,  and 
J-^  for  several  years  excited  much  attention,  both  on 
the  continent  and  in  Great  Britain.  But  he  followed 
quite  closely  in  the  tracks  of  Wright  and  Kant.  Though 
his  style  was  popular,  he  claimed,  like  Kant,  to  found  his 
conjectures  on  substantial  scientific  data.  His  motor 
principle  was  universal  attraction.  Finding  within  our 
planetary  system  residual  phenomena,  especially  as  made 
known  by  Lalande  in  the  systems  of  Jupiter  and  Saturn, 
which  could  not  be  referred  to  causes  within  the  system, 
he  concluded  that  they  must  be  attributable  to  influences 
exerted  from  without.  Unlike  Kant,  he  regarded  the 
comets  as  strangers,  or  at  best  but  naturalized  sojourn- 
ers  in  the  solar  system.  They  constitute  the  material 
proof  of  the  extension  of  the  laws  of  attraction  into  the 
domain  of  the  fixed  stars.  He  felt,  therefore,  fully  con- 
firmed in  an  opinion  which  he  had  long  entertained,  "that 
our  planetary  system  is  only  the  system  of  satellites  of 
another  celestial  body."f  Accordingly,  as  each  of  the 

*Johann  Heinrich  Lambert:  Kosmologische  Briefe  fiber  die  Einrichtung 
des  Weltbam,  Augsburg,  1761,  8vo.  Part  of  these  letters  were  translated  by  the 
author  as  Lettres  Cosmologiques  and  published  in  the  Journal  Helvelique  de 
N-fuchdtel,  1763-4;  an  extract  also,  by  Merian  under  the  title,  Systime  du  Monde, 
Bouillon,  1770,  8vo;  also  complete  translation  by  d'Arquier,  Amsterdam,  1801, 
8vo.  A  portion,  also,  as  Cosmologlcal  Letters,  London,  1828.  The  substance  of 
Dr.  Lambert's  speculations  is  given  by  Prof.  S.  Newcomb:  Popular  Astronomy, 
465. 

t  Letter  to  Bockman.  Correspondance,  annee  1773. 


598        DE.  LAMBERT   AND   SIR   WILLIAM    HERSCHEL. 

planets  is,  or  may  be,  the  centre  of  a  system  of  re- 
volving orbs,  and  the  sun  is  the  centre  of  the  plane- 
tary system,  so  the  planetary  system  with  other  similar 
systems,  must  revolve  about  some  centre  sufficiently 
massive  to  control  its  motions.  Each  star  in  the  heav- 
ens is  the  sun  of  a  planetary  system  ;  and  in  the  clus- 
ters and  constellations  we  see  associated  suns  revolv- 
ing probably  with  a  common  motion  about  their  common 
centres.  This  vast  assemblage  of  solar  systems  consti- 
tutes a  system  of  a  still  higher  order,  which  we  know 
as  the  Milky  Way,  or  Firmament.  Still  beyond  this  are 
other  great  systems  or  galaxies  in  endless  succession,  in- 
visible to  us  only  in  consequence  of  their  immense  dis- 
tances. The  central  masses,  unlike  Kant,  he  conceived 
to  be  dark  and  solid  bodies,  rendered  invisible  by  their 
opacity. 

This  condensed  statement  indicates  that  Kant  ap- 
proached much  more  nearly  than  Lambert  to  the  modern 
conception  of  a  nebular  theory  of  the  planetary  system.* 

§  2.     SIR  WILLIAM  HERSCHEL'S  RESEARCHES^ 

1.  The  Structure  of  the  Heavens. —  Sir  William  Her- 
schel  found  himself,  through  his  own  extraordinary  inge- 
nuity and  energy,  in  possession  of  telescopes  of  power 
unparalleled  in  previous  times.  His  attention  was  accord- 
ingly directed  chiefly  to  the  nature  of  the  fixed  stars  and 

*  Johann  Elert  Bode,  in  an  Introduction  to  Stellar  Astronomy,  entitled  An- 
Ititvng  zur  Kentniss  des  gestirnten  Himmtls,  Hamburg,  circa  1767,  reproduced 
the  conceptions  then  current  froin  the  writings  of  Kant  and  Lambert.  Many 
editions  of  this  work  have  appeared  —  the  seventh  at  Berlin.  1800. 

t  These  researches  are  contained  in  the  Philosophical  Transactions  of  the 
Royal  Society  of  London,  from  1783  to  1818 ;  but  especially  for  the  years  1784, 
1785,  1791,  1795,  1811  and  1814.  A  digest  of  this  work  is  given  by  Arago:  Analyse 
ites  TravauxdeSir  William  Herschel,  in  Anmiaire  du  Bureau  des  Longitudes; 
and  a  brief  account  is  contained  in  NewcombV  Popular  Astronomy,  465-74  and 
495.  Compare,  also,  Sir  John  F.  W.  Herschel :  Observations  of  Nebula  and 
Clusters  of  Stars,  Made  at  Slough  with  a  Twenty-feet  Reflector,  between  the  Ytars 
1825  and  1333,  Philosophical  Transactions,  Nov.  21,  1&33.  Prof.  Holden's  "  Life  " 
of  Sir  William  Herschel  I  have  not  seen. 


SIR  WILLIAM  HERSCHEL'S  RESEARCHES.         599 

the  constitution  of  the  stellar  and  nebular  system.  In 
1784*  he  announced  that  the  sun  must  be  included  in  the 
great  stratum  of  the  Milky  Way.  He  explained  his 
method  of  gauging  the  depths  of  the  firmament,  based  on 
the  assumption  that  the  stars  are  somewhat  uniformly 
distributed  through  space.  On  such  an  assumption  the 
number  of  stars  exhibited  within  the  field  of  his  tele- 
scope would  be  an  indication  of  the  depth  of  the  firma- 
ment in  the  direction  of  the  line  of  sight.  He  concluded, 
as  Kant  had  already  done,  that  the  greatest  dimension  of 
the  firmament  is  in  the  direction  of  the  Milky  Way.  Our 
firmament  may  be  regarded  as  a  flattened  spheroidal 
assemblage  of  stars,  having  our  sun  near  the  centre,  but 
not  entirely  symmetrical  in  its  contour.  In  the  direction 
of  the  galaxy  the  depth  of  the  firmament,  with  the  conse- 
quent number  of  stars  lying  in  the  line  of  sight,  renders 
many  of  the  individual  stars  undistinguishable,  and  pro- 
duces that  cloud-like  diffused  luminosity  characteristic  of 
the  galactic  belt.  On  the  sides,  however,  the  diffused 
light  is  wanting,  the  stars  are  less  numerous,  and  the 
depth  of  the  firmament  must,  therefore,  be  considered  less. 
In  the  following  year  appeared  one  of  Herschel's  most 
important  papers  on  the  constitution  of  the  visible  uni- 
verse, f  He  presents  a  "theoretical  view"  in  the  follow- 
ing words:  "Let  us  then  suppose  numberless  stars  of 
various  sizes  scattered  over  an  indefinite  portion  of  space 
in  such  a  manner  as  to  be  almost  equally  distributed 
throughout  the  whole.  The  laws  of  attraction,  which  no 
doubt  extend  to  the  remotest  regions  of  fixed  stars,  will 
operate  in  such  a  manner  as  most  probably  to  produce  the 
following  remarkable  effects,"  which  he  styles  "the  for- 
mation of  nebulas"  —  an  expression  which  reflects  the 

*  Of  Some  Observations  Tending  to  Investigate  the  Constitution  of  the 
Heavens,  Phil.  Trans.,  vol.  Ixxiv,  437. 

t  On  the  Construction  of  the  Heavens,  Phil.  Trans.,  1785,  vol.  Ixxv,  p.  213. 


600        DR.  LAMBERT    AND   SIR    WILLIAM    HERSCHEL. 

opinion  then  held  by  him,  that  all  the  nebula?  are  clusters 
of  stars  like  our  own  firmament,  but  all  external  to  it, 
and  in  many  cases  "  unresolvable  "  only  in  consequence  of 
their  enormous  distances.  He  conceives  that  forms  like 
the  following  must  result:  Form  1.  A  large  star  draws 
surrounding  smaller  ones  toward  it,  and  a  cluster  with  a 
globular  figure  results.  Form  2.  A  few  stars,  closer 
together  than  the  average,  constitute  a  central  attractive 
group.  From  this  process  a  great  variety  of  shapes 
might  result.  Form  3.  Produced  by  the  "composition 
and  repeated  conjunction  of  both  the  foregoing  forms." 
The  result  would  be  "long-extended,  regular  or  crooked 
rows,  hooks  or  branches."  Form  4.  Still  more  extensive 
combinations,  when,  at  the  same  time  that  a  cluster  of 
stars  is  forming  in  one  part  of  space,  there  may  be  an- 
other collecting  in  a  different,  but  perhaps  not  far  distant 
quarter,  which  may  occasion  a  mutual  approach  toward 
their  common  centre  of  gravity."*  Form  5.  "As  a 
natural  consequence  of  the  former  cases,  there  will  be 
formed  great  cavities  or  vacancies  by  the  retreat  of  the 
stars  toward  various  centres  which  attract  them." 

He  then  replies  to  certain  objections  which  might  be 
offered  against  such  conceptions.  Such  an  arrangement, 
it  might  be  said,  tends  to  "general  destruction  by  the 
shock  of  one  star's  falling  on  another."  He  replies:  1. 
The  Creator  has  the  power  to  avert  such  destruction,  and 
conserve  the  celestial  order  by  some  method  not  known  to 
us.  2.  "The  indefinite  extent  of  the  sidereal  heavens 
must  produce  a  balance  that  will  effectually  secure  all  the 
great  parts  of  the  whole  from  approaching  to  each  other." 
The  stars  may  also  have  had  an  original  force  of  pro- 
jection, and  this  would  secure  perpetuity  to  each  cluster 
"at  least  for  millions  of  ages."  "Besides,  we  ought,  per- 

*  These  specifications  are  similar  to  those  presented  in  the  present  work, 
Part  I,  ch.  ii,  except  that  the)'  are  applied  to  the  congregation  of  stars  instead 
of  the  aggregation  of  nebulous  matter. 


SIR  WILLIAM  HERSCHEL'S  RESEARCHES.         601 

haps,  to  consider  such  clusters  and  the  destruction  of  now 
and  then  a  star,  in  some  thousands  of  ages,  as  perhaps  the 
very  means  by  which  the  whole  is  preserved  and  renewed. 
These  clusters  may  be  the  laboratories  of  the  universe,  if 
I  may  so  express  myself,  wherein  the  most  salutary  reme- 
dies for  the  decay  of  the  whole  are  prepared." 

Herschel  then  presents  further  details  of  results  of 
star  gauging,  with  confirmations  of  his  former  conclusions 
respecting  our  star  cluster. 

2.  Nebular  Studies. — The  unequal  distribution  of  the 
nebulas  receives  his  attention.  Those  regions  in  which  the 
nebulas  are  most  evenly  scattered  possess  "  a  certain  air  of 
youth  and  vigor."  The  stellar  bodies  have  not  yet  had 
sufficient  time  to  withdraw  themselves  from  wide  spaces 
in  their  process  of  general  aggregation.  The  nebular  forms 
of  the  first  and  second  class  "  probably  owe  their  origin  to 
what  may  be  called  the  decay  of  a  great  compound  nebula 
of  the  third  class;  and  the  subdivisions  which  have  hap- 
pened to  them  in  length  of  time  have  occasioned  all  the 
small  nebulas  which  spring  from  them  to  lie  in  a  certain 
range,  according  as  they  are  detached  from  the  primary 
one.  In  like  manner,  our  system,  after  numbers  of  ages, 
may  very  probably  become  divided  so  as  to  give  rise  to  a 
stratum  of  two  or  three  hundred  nebulas;  for  it  would  not  be 
difficult  to  point  out  so  many  beginning  or  gathering  clus- 
ters in  it."  Some  parts  of  our  firmament  indeed,  begin 
to  show  the  "  ravages  of  time,"  for  the  stellar  bodies  have 
been  almost  completely  withdrawn  from  them.  One  of 
these  remarkable  "openings  in  the  heavens"  exists  in 
the  Scorpion,  Other  parts  present  a  wonderful  degree 
of  "purity  or  clearness,"  and  this  is  the  general  aspect 
of  the  sky  "  when  we  look  out  of  our  stratum  at  the 
sides." 

In  this  connection  he  enumerates  several  other  Milky 
Ways  or  firmaments,  some  of  which  are  supposed  to  be 


602        DR.  LAMBERT   AND    SIR    WILLIAM    HERSCHEL. 

much  larger  than  our  own,  and  one  of  which  presents  the 
aspect  of  a  ring  of  stars.  "  Planetary  nebulae  "  are  par- 
ticularly noticed.  They  present,  unlike  ordinary  nebulae, 
a  uniform  brightness  from  side  to  side.  Their  "  light, 
however,  seems  to  be  of  a  starry  nature,  which  suffers  not 
nearly  so  much  as  the  planetary  discs  are  known  to  do 
when  much  magnified."  Their  light  is  uniform  and  vivid. 
Their  diameters  are  too  small  for  nebulas;  and  their 
brightness  is  too  persistent  under  high  powers,  to  be  of  a 
planetary  character,  while  it  is  not  intense  enough  for 
fixed  stars.  They  are  probably  nebulas;  "but  then  they  must 
consist  of  stars  that  are  compressed  and  accumulated  in 
the  highest  degree.  If  it  were  not  perhaps  too  hazardous 
to  pursue  a  former  surmise  of  a  renewal  in  what  I  fig- 
uratively called  the  laboratories  of  the  universe,  the  stars 
forming  these  extraordinary  nebulas,  by  some  decay  or 
waste  of  nature  being  no  longer  fit  for  their  former  pur- 
poses, and  having  their  projectile  forces,  if  any  such  they 
had,  retarded  in  each  other's  atmosphere,  may  rush  at  last, 
together,  and  either  in  succession,  or  by  one  general  and 
tremendous  shock,  unite  into  a  new  body.  Perhaps  the 
extraordinary  and  sudden  blaze  of  a  new  star  in  Cas- 
siopoeia's  Chair,  in  1572,  might  possibly  be  of  such  a 
nature."* 

Hitherto,  Herschel  had  considered  all  the  nebulas  as 
merely  clusters  of  stars.  Some  of  them  had  been  actually 
resolved  into  points  of  light,  and  their  resolvability  seemed 
to  bear  a  relation  to  the  telescopic  power  employed.  It 
was  perfectly  natural,  therefore,  to  conclude  that  all  would 
show  resolvability  if  instruments  sufficiently  powerful 
could  be  brought  into  use.  But  in  1791f  he  began  to 

"Herschel's  conception  of  the  form  of  our  firmament  is  illustrated  in  Plate 
viii  of  the  volume  of  Transactions  last  cited.  These  figures  are  reproduced  in 
Newcomb's  Popular  Astronomy,  pp.  469  and  481.  For  a  popular  and  brilliant 
exposition  of  Herschel' s  views,  see  Prof.  J.  P.  Nichol:  Views  of  the  Architecture 
of  the  Heavens,  Amer.  ed.,  1842. 

t  On  Nebulous  Stars  Properly  So-called.    Phil.  Trans.,  1791. 


SIR  WILLIAM  HERSCHEL'S  RESEARCHES.         603 

suspect  that  certain  cases  of  diffused  luminosity  could  not 
arise  from  the  blended  light  of  numerous  distant  suns.  The 
"nebulous  stars,"  now  first  observed,  present  a  bright 
central  body  surrounded  by  a  faint  light  cloud.  Now  if 
this  envelope  consists  of  stars,  they  must  be  either  too 
small  to  be  regarded  as  stars,  properly  speaking,  since 
while  the  central  star  is  perfectly  distinct  they  are  indis- 
tinguishable, or  otherwise,  the  central  star  must  attain  a 
magnitude  which  surpasses  credence.  This  subject,  even 
while  researches  of  diverse  nature  occupied  his  time,* 
seems  to  have  been  kept  before  his  attention.  In  1811  he 
presented  one  of  the  most  important  papers  of  the  re- 
markable series  which  resulted  from  his  highly  original 
investigations.!  He  here  formally  announces  a  gradual 
change  of  opinion  in  regard  to  the  resolvability  of  some 
of  the  nebulas.  The  most  primitive  nebular  condition  is 
represented,  he  thinks,  by  the  simple  diffused  nebulosities, 
of  which  he  has  determined  the  positions  of  fifty-two. 
The  brighter  portions  he  regards  as  more  dense,  and  the 
central  condensation  is  due  to  the  action  of  gravity. 
Some  nebulaa  seem  to  have  more  than  one  centre  of  attrac- 
tion; and  some,  it  may  be,  are  even  undergoing  a  process 
of  disintegration.  The  spheroidal  forms  would  naturally 
result  from  the  action  of  a  central  attractive  force.  There 
are  many  in  which  the  central  brightness  indicates  the 

*  In  1795  he  communicated  a  paper  On  the  Construction  of  the  Sun  and  Fixed 
Stars,  in  which  he  recorded  the  opinion  that  many  of  the  stars  are  habitable, 
since  some  are  too  close  to  admit  of  planetary  orbits,  and  that  if  not  habitable 
in  the  character  of  suns  "  many  stars,  unless  we  would  make  them  mere  useless 
brilliant  points,  may  themselves  be  lucid  planets,  perhaps  unattended  by  satel- 
lites." In  1805  he  discussed  The  Direction  and  Velocity  of  the  Motion  of  the  Sun 
and  Solar  System.  (See  also  Phil.  Trans.,  1783,  On  the  Proper  Motion  of  the  Sun 
and  Sotar  System.)  The  conclusion  of  his  researches  on  this  point  is  that  the  sun 
is  moving  toward  the  constellation  Hercules.  In  1806  he  read  a  paper  On  the 
Quantity  and  Velocity  of  the  Solar  Motion. 

t  Astronomical  observations  relating  to  the  construction  of  the  heavens,  ar- 
ranged for  the  purpose  of  a  critical  examination,  the  result  of  which  appears 
to  throw  some  new  light  upon  the  organization  of  the  celestial  bodies. 


604        DR.  LAMBEET    ASTD   SIR   WILLIAM    HERSCHEL. 

seat  of  principal  attraction.  Some  even  have  a  distinct 
central  nucleus.  The  various  degrees  of  condensation  are 
supposed  to  take  place  successively  in  the  same  nebula. 

The  appearance  of  certain  very  regular  nebulae  with 
extensive  branches  suggests  various  queries.  Do  not  the 
branches  connected  with  a  nucleus  resemble  the  zodiacal 
light  connected  with  our  sun?  May  not  portions  of 
branches  collect  into  a  planetary  form  and  revolve  around 
the  central  nucleus  [of  the  nebula],  having  themselves  a 
rotary  motion  in  consequence  of  the  inequality  and  irregu- 
lar position  of  the  different  branches?  Seven  nebula?  are 
mentioned  which  seem  to  have  approached  very  near  to 
final  condensation.  The  spheroidal  form  which  prevails 
among  nebulas  is  something  from  which  a  rotation  on  their 
axes  may  be  inferred. 

That  nebulas  do  really  undergo  successive  changes, 
Herschel  concludes  not  only  from  a  comparison  of  different 
nebula?  with  each  other,  but  from  a  comparison  of  his  own 
observations  made  on  the  nebula  of  Orion  at  this  time, 
with  those  which  he  himself  made  thirty-seven  years  be- 
fore. This  nebula  he  thinks  is  certainly  nearer  than  the 
stars  of  the  seventh  or  eighth  magnitude,  and  it  may  pos- 
sibly not  be  more  distant  than  those  of  the  third. 

He  suggests,  at  this  time,  the  following  gradation 
of  nebular  existences:  1.  Diffused  nebulosity,  invisible 
until  partially  condensed.  2.  Planetary  nebulae,  with  uni- 
form light.  3.  Stellar  nebula?,  having  a  bright  central 
nucleus.  4.  A  complete  star,  all  the  nebulous  matter 
being  condensed. 

In  1814  Herschel's  views  had  become  still  more  clearly 
defined.*  He  shows  that  clusters  of  stars  are  gravitating 
together  like  nebulous  matter.  Some  stars  are  attracting 

*  Astronomical  observations  relating  to  the  sidereal  part  of  the  heavens,  and 
its  connection  with  the  nebulous  part;  arranged  for  the  purpose  of  a  critical 
examination.  Phil.  Trans.,  1814,  p.  248. 


SIR  WILLIAM  HERSCHEL'S  RESEARCHES.         605 

patches  of  nebulous  matter  to  themselves.  Stars  and 
nebulas  seem  to  be  drawn  together  by  mutual  attraction. 
By  additions  of  matter  there  may  be  thus  a  real  growth 
of  stars.  He  mentions  one  hundred  and  fifty  instances 
in  which  clusters  of  stars,  by  being  more  dense  toward  the 
centre,  manifest  a  tendency  like  that  in  nebula?.  He  sug- 
gests now,  the  following  gradation  in  nebular  development: 
1.  Globular  nebula.  2.  Nebula  with  nucleus.  3.  Nebu- 
lous star.  4.  Distinct  star  surrounded  by  a  nebulosity. 
5.  The  perfect  simple  star. 

In  1817  and  1818*  Herschel  returned  to  the  work  of 
sounding  the  depths  of  the  firmament,  basing  his  conclu- 
sions on  the  assumption  that  the  distances  of  the  stars  are 
on  the  whole  inversely  proportional  to  their  brightness. 
He  concludes,  as  the  result  of  these  renewed  researches, 
that  his  former  determinations  do  not  require  material 
alteration,  and  that  little  further  knowledge  is  attainable 
in  reference  to  the  form  and  depth  of  our  firmament, 
especially  in  the  direction  of  the  Milky  Way.f 

*  Astronomical  observations  and  experiments  tending  to  investigate  the  local 
arrangement  of  the  celestial  bodies  in  space  and  to  determine  the  extent  and 
condition  of  the  Milky  Way.  Phil.  Trans.,  1817,  p.  302.  Astronomical  observa- 
tions and  experiments  selected  for  the  purpose  of  ascertaining  the  relative  dis- 
tances of  clusters  of  stars,  and  of  investigating  how  far  the  powtr  of  our  tele- 
scopes may  be  expected  to  reach  into  space  when  directed  to  ambiguous  celestial 
objects,  Phil.  Trans.,  1818. 

t  Sir  John  Herschel,  in  communicating  to  the  Royal  Soeiety,  Observations  of 
nebu'.ce  and  clusters  of  stars  made  at  Slough  with  a  twenty -feet  reflector,  between 
the  years  18S5  and  1S33  (Phil.  Trans.,  Nov.  91, 1833)  supplies  an  appendix  to  his 
father's  researches.  He  transmits  a  catalogue  of  2,500  nebulie  and  clusters,  of 
which  2,000  had  been  previously  reported  by  his  father.  The  most  remarkable 
nebulae  were  accompanied  by  sketches.  "Among  these  are  represented  some 
very  extraordinary  objects  which  have  not  hitherto  sufficiently  engaged  the  at- 
tention of  astronomers,  and  many  of  which  possess  a  symmetry  of  parts  and  a 
unity  of  design  strongly  marking  them  as  systems  of  definite  nature,  each  com- 
plete in  itself,  subservient  to  some  distinct,  though  to  us  inscrutable  purpose.'' 


CHAPTER  IY. 

LAPLACE'S    SYSTEM    OF    THE    WORLD.* 

France  possesses  an  immortal  work,  L' Exposition  du,  Systeme  du  Monde,  in 
which  the  author  has  combined  the  results  of  the  highest  astronomical  and 
mathematical  labors,  and  presented  them  to  his  readers  free  from  all  processes 
of  demonstration.  The  structure  of  the  heavens  is  here  reduced  to  the  simple 
solution  of  a  great  problem  in  mechanics ;  yet  Laplace's  work  has  never  yet  been 
accused  of  incompleteness  and  want  of  profundity.— HUMBOLDT. 

§  1.   PRELIMINARY  VIEWS  ON  NEBULJS  AND  GENERAL* 
PHYSICAL  ASTRONOMY. 

THE  purpose  of  this  work  is  to  present  in  popular  style 
the  general  results  of  astronomical  research.  It  de- 
scribes the  apparent  movements  of  the  heavenly  bodies  and 
their  real  movements,  proceeding  thence  to  an  exposition 
of  the  mechanical  laws  of  their  movements,  and  of  the 
theory  of  universal  gravitation,  and  of  its  operation  in 
the  forms  and  interactions  of  the  planetary  masses.  The 
last  book  is  devoted  to  an  epitome  of  the  history  of 
astronomy,  in  the  last  chapter  of  which  the  author  pre- 
sents some  general  reflections,  and  records  some  remark- 
able anticipations  of  future  discoveries. 

He  expresses  the  opinion  that  some  of  the  other 
planets  may  be  the  abodes  of  animals  and  plants  analo- 
gous to  those  which  exist  upon  the  earth  ;  but  the  great 
diversities  of  temperature  must  necessitate  a  remarkable 
diversity  of  organization.  The  physical  relations  which 

*  Pierre  le  Marquis  de  Laplace:  Exposition  du  Systime  du  Monde,  5me  ed. 
revue  et  augmenlee  par  Tauteur.  Paris,  1824.  4to,  pp.  419.  The  original  edition 
was  published  in  two  vols.  8vo,  Paris,  17%,  and  the  sixth  edition,  containing  a 
eulogy  by  Baron  Fourier,  in  4to,  1835,  eight  years  after  Laplace.'s  death.  An 
English  translation  exists. 


PKELIMINABY    VIEWS   ON.    NEBULA,  ETC.  607 

exist  among1  the  planets  shed  much  light  upon  their 
origin.  The  astonishing  number  of  uniformities  enum- 
erated could  not  arise  from  any  irregular  causes.  Sub- 
jecting the  question  to  computation,  it  appears  that  the 
probability  is  more  than  two  hundred  trillions  to  one  that 
these  harmonies  are  not  the  result  of  chance.  "It  is 
necessary,  therefore,  to  assume  that  one  primitive  cause 
has  directed  all  the  planetary  movements."  Another  re- 
markable fact  is  the  small  eccentricity  of  the  planetary 
orbits.  There  is  no  intermedium  between  the  planets  and 
the  comets  in  this  respect.  "What  is  that  primitive 
cause  ?  I  shall  offer  a  hypothesis  in  the  note  at  the  end 
of  this  work,  which  appears  to  me  to  result,  with  great 
probability,  from  the  preceding  phenomena  ;  but  I  pre- 
sent it  with  the  diffidence  which  ought  to  inspire  every- 
thing which  is  not  the  result  of  observation  or  of  calcu- 
lation." 

Before  proceeding  to  reproduce  the  substance  of  the 
note,  I  think  it  proper  to  follow  the  author  in  some  of  his 
general  considerations,  since,  as  will  appear,  they  are 
connected  with  his  hypothesis,  although  not  made  to 
constitute  a  part  of  it.  Some  of  the  phenomena  of  our 
system  Newton  confessed  his  inability  to  refer  to  the  prin- 
ciple of  gravitation.  Such  were  the  uniformity  in  the 
directions  of  planetary  movements,  the  nearly  circular 
forms  of  the  orbits,  and  their  remarkable  conformity  to 
one  plane.  These  adjustments  Newton,  in  his  general 
scholium,*  pronounces  to  be  "the  work  of  an  intelligent 
and  all-powerful  Being."  "But,"  asks  Laplace,  "might 
not  these  arrangements  be  an  effect  of  the  laws  of 
motion  ;  and  might  not  the  supreme  intelligence  which 
Newton  invoked  have  caused  them  to  depend  on  a  more 

*  Laplace  in  a  note  says;  "This  scholium  is  not  found  in  the  first  edition  of 
Newton's  work.  It  appears  that  Newton  to  that  time  was  devoted  exclusively 
to  the  mathematical  sciences  which,  unhappily  for  them  and  for  his  own  fame, 
be  too  soon  abandoned," 


608  LAPLACE'S  SYSTEM  OF  THE  WOULD. 

general  phenomenon  ?  Such  is,  according  to  our  con- 
jectures, that  of  a  nebulous  matter  dispersed  in  masses 
through  the  immensity  of  the  heavens.  Is  it  possible 
then  to  affirm  that  the  conservation  of  the  planetary  sys- 
tem enters  into  the  views  of  the  author  of  nature  ?  The 
mutual  attraction  of  the  bodies  of  this  system  cannot 
alter  its  stability,  as  Newton  himself  demonstrated  ;  but 
there  may  be  in  celestial  space  some  other  fluid  than 
light;  its  resistance,  and  the  diminution  which  its  emis- 
sion causes  in  the  mass  of  the  sun,  must  at  length  destroy 
the  arrangement  of  the  planets,  and,  to  maintain  it,  a  re- 
constitution  would  undoubtedly  become  necessary.  But 
do  not  the  numerous  species  of  extinct  animals  whose  or- 
ganization Mr.  Cuvier  has  determined  with  such  rare 
sagacity,  in  the  numerous  fossil  bones  which  he  has  de- 
scribed, indicate  a  tendency  in  nature  to  change  even 
those  things  which  appear  most  permanent?  The  gran- 
deur and  importance  of  the  solar  system  ought  not  to 
constitute  an  exception  to  this  general  law,  for  they  exist 
only  relatively  to  our  insignificance,  and  this  system,  vast 
as  it  seems,  is  only  an  insensible  point  in  the  universe. 
Glance  over  the  history  of  the  progress  of  the  human 
mind  and  its  errors,  and  we  see  there  final  causes  continu- 
ally retreating  before  the  bounds  of  human  knowledge. 
Those  causes  which  Newton  removed  to  the  limits  of  the 
solar  system  were,  even  in  his  time,  located  in  the  atmos- 
phere for  the  explanation  of  meteors.  They  are  nothing, 
then,  in  the  eyes  of  the  philosopher,  but  the  expression 
of  our  ignorance  of  true  causes."*  Casting  our  eyes  be- 

*  This  passage  shows  that  by  "final  causes"  Laplace  understood  that  der- 
nier resort  to  which  we  all  come  at  last  —  the  most  learned  philosopher  as  well 
as'the  medieval  religionist — where  actual  knowledge  can  furnish  no  further  ex- 
planation, and  judgment  and  reason  together  fall  hack  on  an  inscrutable  world- 
making  agency.  "Final  causes  "—last  causes— are  simply  the  antithesis  of 
known  and  explicable  causes  — that  is,  explicable  as  to  their  modes  of  operation. 
Now,  in  this  sense,  it  is  obviously  unsafe  to  declare  at  any  stage  in  the  exten- 
sion of  our  knowledge,  that  uiind  will  make  no  further  advance,  and  that  all 


PRELIMINARY   VIEWS   ON   NEBULAE,  ETC.  609 

yond  the  limits  of  the  solar  system,  the  changes  observed 
in  the  color  and  brightness  of  certain  stars  show  that 
the  principle  of  permanence  cannot  be  of  universal  ap- 
plication. The  temporary  star  described  by  Tycho  Brahe 
convinces  us  that  in  the  depths  of  space  revolutions  occur 
which  surpass  beyond  computation  all  which  take  place 
on  the  surface  of  the  earth.  As  this  star  did  not  cease  to 
exist  after  it  became  invisible,  we  are  taught  that  other 
equally  considerable,  but  dark  and  invisible,  bodies,  may 
exist  in  number  perhaps  equal  to  the  number  of  the  stars. 
The  heavenly  bodies  are  undoubtedly  assembled  in  groups. 
The  group  to  which  our  sun  belongs  seems  to  encircle  the 
heavens  as  a  Milky  Way.  Like  the  Milky  Way,  many  of 
the  nebulae  are  probably  assemblages  of  stars  which  to  a 
beholder  from  their  interiors  would  seem  like  other  galaxies. 

beyond  is  simply  the  product  of  "final  causation" — that  is,  of  divine  causation. 
If  this  were  the  only  conception  of  final  cause,  we  should  truly  be  compelled  to 
abandon  the  search  for  it;  and  yet  every  intelligent  person  would  feel  con- 
strained to  admit  that  somewhere  is  an  ultimate  limit  to  the  activity  of  sec- 
ondary causation  (physical  antecedence  and  sequence)  and  a  real  beginning  pro- 
ceeding out  of  some  activity  which  is  supernatural. 

But  the  term  "final  cause"  has  a  more  legitimate  signification  which  fur- 
nishes something  worth  contending  for.  It  implies,  that  in  the  exertion  of  that 
primitive  supernatural  causation  there  must  have  been  some  purpose  present. 
It  implies,  therefore,  that  iu  the  endless  series  of  events  which  flow  from  that 
primitive  causal  act  that  primitive  purpose  is  ever  unfolding  and  ever  present. 
It  does  not  imply  that  in  any  specific  result  finite  intelligence  can  certainly 
eliminate  the  specific  divine  purpose;  but  it  does  imply  that  in  every  specific 
result  there  is  some  divine  purpose. 

If,  as  modern  physics  tend  to  conclude,  the  physical  forces  are  only  the 
manifestations  of  a  supreme  will,  exerted  according  to  a  predetermined  method, 
then  each  specific  and  individual  result  will  associate  with  it  directly,  the  neces- 
sary conception  of  purpose,  just  as  that  conception  is  always  inseparable  from 
primitive  causation. 

It  is  only  a  superficial  and  unsatisfactory  science  which  contents  itself  with 
the  observation  and  collocation  of  mere  phenomena,  and  the  determination  of 
the  methods  according  to  which  they  emerge  into  existence.  The  human  mind 
demands  causes  —  and  not  alone  physical  causes  or  mere  uniform  antecedents  — 
but  real  ultimate  causes,  "metaphysical  causes."  I  maintain,  therefore,  that 
every  normally  active  intellect  tends  toward  metaphysical  conceptions  of 
material  phenomena.  (See  an  article  by  the  present  writer  on  The  Metaphysics 
of  Science,  in  North  American  Review,  Jan.,  1880,  also,  Sparks  from  a  Geolo- 
gist's Hammer,  pp.  358-85.) 


610  LAPLACE'S  SYSTEM  OF  THE  WOULD. 

Herschel  has  followed  the  progressive  changes  in  neb- 
ulae, as  we  trace  the  life  history  of  a  tree,  by  observation 
of  successive  states  contemporaneously  existing  in  differ- 
ent trees.  His  classification  of  nebulas  is  then  cited,*  and 
particular  attention  is  directed  to  the  stellar  nebulae  in 
which  a  well  marked  nucleus,  or  several  of  them,  has 
already  come  into  existence.  The  atmosphere  of  each 
nucleus  seems  to  be  condensing  upon  the  centre.  When 
the  matter  condenses  uniformly,  a  planetary  nebula  re- 
sults. The  phenomena  indicate  with  great  probability  a 
progressive  transformation  into  stars,  and  imply  that  exist- 
ing stars  were  at  a  former  time  nebulas.  "Thus  we 
descend  through  the  process  of  condensation  of  nebulous 
matter  to  the  consideration  of  the  sun  surrounded  at  a 
former  time  by  a  vast  atmosphere,  a  conception  to  which 
I  have  already  been  led  by  a  consideration  of  planet- 
ary phenomena,  as  will  appear  in  the  note  before  referred 
to.  A  coincidence  so  remarkable  in  pursuing  opposite 
courses  gives  to  the  existence  of  this  former  condition  of 
the  sun  a  high  degree  of  probability."! 

"In  connecting  the  formation  of  comets  with  that  of 
nebulas,  we  may  regard  them  as  small  nebulas  wandering 
from  solar  system  to  solar  system,  and  formed  by  the 
condensation  of  nebulous  matter  dispersed  with  so  great 
profusion  through  the  universe.  Comets  would  thus  be, 
in  relation  to  our  system,  what  aerolites  are  in  relation 
to  the  earth,  to  which  they  are  strangers"  *  *  *  "This 

*  See  above,  p.  604. 

t  It  is  often  alleged  by  the  opponents  of  the  nebular  theory  that  its  author 
—  meaning  Laplace  —  placed  a  low  estimate  on  its  importance  and  probability, 
and  therefore  hid  it  away  in  a  note  at  the  end  of  the  volume.  But  such  expres- 
sions as  that  above  quoted,  and  others  hereafter  to  be  quoted,  indicate  that 
Laplace  regarded  his  hypothesis  as  possessing  great  strength.  Moreover,  many 
of  the  accessory  facts  and  reasonings  are  embodied  in  the  leading  discussions 
of  his  work.  More  than  a  quarter  of  a  century  after  the  publication  of  the 
work,  the  author  referred  to  this  theory  with  a  degree  of  complacency  which 
showed  that  years  had  ripened  the  conviction  of  its  tenability  and  value.— Me- 
canique  Celeste,  torn,  v,  346. 


HYPOTHESIS   OF  GENESIS  OP  SOLAR   SYSTEM.        611 

hypothesis  explains  in  a  happy  mariner  the  enlargement 
undergone  by  the  heads  and  tails  of  comets  in  their  ap- 
proach to  the  sun;  the  extreme  rarity  of  their  tails,  which, 
notwithstanding  their  immense  thickness,  do  not  sensibly 
diminish  the  light  of  the  stars  seen  through  them;  the 
varied  directions  of  the  motions  of  comets,  and  the  high 
eccentricity  of  their  orbits." 

The  movements  revealed  in  the  solar  system  are  exceed- 
ingly complicated.  Like  the  planets,  however,  the  stars 
are  also  in  motion.  The  sun  describes  an  epicycloidal 
orbit  around  the  centre  of  gravity  of  the  universe.  Ages 
must  be  demanded  to  enable  us  to  determine  precisely  the 
movements  of  the  sun  and  the  other  stars:  but  observa- 
tion has  already  shown  that  the  stars  have  real  motions, 
while  some  of  the  double  stars  are  proved  to  possess  orbital 
movements  about  a  common  centre  of  gravity;  and  even 
the  nebulae,  especially  that  in  Orion,  have  been  observed 
in  progress  of  change.  Such  phenomena  will  present  to 
the  astronomy  of  the  future  its  principal  problems. 

§  2.     HYPOTHESIS  TOUCHING  THE  GENESIS  OP  THE 
SOLAR  SYSTEM. 

We  come  now  to  the  contents  of  the  celebrated  Note. 
Its  scope  embraces  only  the  solar  system,  but  we  have 
seen  that  the  grounds  of  the  hypothesis  are  supplied  in 
the  facts  of  positive  astronomy  in  all  its  range.  Buffon 
attempted  to  explain  the  origin  and  phenomena  of  the 
solar  system  by  supposing  that  a  comet  had  struck  the 
sun  and  detached  a  torrent  of  matter  which  gathered  in 
planetary  g'lobes  more  or  less  removed,  and  in  course  of 
time  became  cold  and  opaque.  While  this  hypothesis 
explains  many  of  the  phenomena  cited,  it  does  not  ex- 
plain why  the  planet  rotates  in  the  same  direction  as  its 
orbital  motion,  nor  why  the  eccentricity  of  its  orbit  should 
be  so  low.  Theory  shows  that  if  it  were  thrown  off  from 


612  LAPLACE'S  SYSTEM  OF  THE  WOULD. 

the  sun  it  would  periodically  return  nearly  to  the  same 
point.  Finally,  the  hypothesis  of  Buffon  does  not  explain 
the  abrupt  transition  in  respect  to  eccentricity  between 
the  orbits  of  the  planets  and  those  of  the  comets. 

1.  Former  Expansion  of  the  Solar  Atmosphere.  — 
"  Whatever  the  nature  of  the  common  cause  of  the  planet- 
ary movements,  since  it  has  produced  or  directed  these 
movements  it  must  of  necessity  have  embraced  all  the 
planetary  bodies;  and,  considering  the  prodigious  dis- 
tances which  separate  them,  it  could  have  been  nothing 
else  than  a  fluid  of  immense  extent.  In  order  to  have 
given  them  an  almost  circular  motion  in  a  uniform  direc- 
tion about  the  sun,  this  fluid  must  have  surrounded  the 
solar  body  like  an  atmosphere.  The  consideration  of  the 
planetary  movements  leads  us,  then,  to  think  that,  in  con- 
sequence of  its  excessive  heat,  the  atmosphere  of  the  sun 
extended  formerly  beyond  the  orbits  of  all  the  planets, 
and  that  it  contracted  by  degrees  to  its  present  limits." 

"In  this  primitive  state  of  the  sun  it  resembled  the 
nebulae  which  the  telescope  reveals  to  us  composed  of  a 
more  or  less  brilliant  nucleus,  surrounded  by  a  nebulosity 
which,  by  condensation  upon  the  surface  of  the  nucleus, 
transforms  it  into  a  star.  If,  by  analogy,  we  conceive  all 
the  stars  formed  in  this  manner,  we  can  imag'ine  their 
former  state  of  nebulosity  itself  preceded  by  other  states 
in  which  the  nebulous  matter  was  more  and  more  diffuse, 
the  nucleus  being  less  and  less  luminous.  We  arrive  thus, 
in  receding  as  far  as  possible,  at  a  nebulosity  so  diffuse  that 
its  existence  is  barely  imaginable." 

Mitchel  long  since  remarked  that  the  grouping  of  the 
Pleiades  could  not  be  the  result  of  chance;  and  the  same 
may  be  said  of  all  clusters  of  stars.  They  must  be  "the 
effects  of  a  primitive  cause  or  general  law  of  nature. 
Such  groups  are  the  necessary  result  of  the  condensation 
of  nebulae  about  numerous  nuclei." 


HYPOTHESIS   OF   GENESIS   OF   SOLAR   SYSTEM.       613 

2.  Formation  and  Abandonment  of  Zones  of  Vapor. 
— "  But  how  did  the  solar  atmosphere  determine  the  mo- 
tions of  rotation  and  revolution  of  the  planets  and  satel- 
lites? If  these  bodies  had  been  profoundly  immersed  in 
this  atmosphere,  its  resistance  would  have  caused  them  to 
fall  upon  the  sun.  We  are  compelled  to  assume,  there- 
fore, that  the  planets  have  been  formed  at  their  successive 
limits  by  the  condensation  of  zones  of  vapors  which,  in 
the  process  of  cooling,  it  must  have  abandoned  in  the 
plane  of  its  equator." 

"  Let  us  recall  now  the  results  presented  in  the  tenth 
chapter  of  the  preceding  book.  The  atmosphere  of  the 
sun  could  not  extend  outward  indefinitely;  its  limit  would 
be  the  point  where  the  centrifugal  force  due  to  its  move- 
ment of  rotation  would  counterbalance  gravitation.  But, 
in  proportion  as  cooling  contracted  the  atmosphere,  and 
condensed  at  the  surface  of  the  body  the  molecules  located 
in  that  region,  the  movement  of  rotation  increased  by 
virtue  of  the  principle  of  areas."  The  centrifugal  force 
due  to  increased  rotation  becoming  increased,  the  point 
where  gravity  equals  it  would  be  nearer  the  centre.  In 
short,  a  process  of  annulation  would  begin  and  proceed.* 

The  zones  of  vapors  necessarily  abandoned  "must 
probably,  by  their  condensation  and  the  mutual  attraction 
of  their  molecules,  have  formed  different  concentric  rings  of 
vapors  circulating  about  the  sun.  The  mutual  friction  of 
the  molecules  of  each  ring  must  have  accelerated  some 
and  retarded  others,  until  all  should  have  acquired  the 
same  angular  motion.  Thus  the  actual  velocities  of  the 
molecules  most  remote  from  the  sun  have  been  the  greater. 
The  following  cause  must  have  further  contributed  to  this 
difference  of  velocities:  The  molecules  farthest  removed 
from  the  sun,  and  which,  in  the  progress  of  cooling  and 
condensation,  must  have  formed  the  exterior  portion  of 

*  In  the  way  which  I  have  elsewhere  explained,  following  Laplace. 


614  LAPLACE'S  SYSTEM  OF  THE  WOELD. 

the  ring,  have  always  described  areas  proportional  to  the 
times,  since  the  central  force  which  actuated  them  has 
been  constantly  directed  toward  the  solar  centre;  but  this 
constancy  of  areas  demands  an  acceleration  of  velocity  in 
proportion  as  the  molecules  are  condensed.  It  is  apparent 
that  the  same  cause  must  have  diminished  the  velocity  of 
the  molecules  which  constitute  the  interior  border  of  the 
ring." 

3.  Rupture  and  Planetation  of  Rings. —  Proceeding 
to  the  subsequent  history  of  a  ring,  the  author  shows  that 
the  conditions  of  its  permanence  can  very  rarely  exist. 
"Almost  always  each  ring  of  vapors  must  have  broken  up 
into  numerous  masses,  which,  moving  with  a  nearly  uni- 
form velocity,  must  have  continued  to  circulate  at  the 
same  distance  around  the  sun.  These  masses  must  have 
taken  a  spheroidal  form,  with  a  motion  of  rotation  in  the 
same  direction  as  their  revolution,  since  the  inner  mole- 
cules [those  nearest  the  sun]  would  hare  less  actual 
velocity  than  the  exterior  ones.  They  must  then  have 
formed  as  many  planets  in  a  state  of  vapor.  But  if  one 
of  them  was  sufficiently  powerful  to  unite  successively,  by 
its  attraction,  all  the  others  around  its  centre,  the  ring  of 
vapors  must  have  been  thus  transformed  into  a  single 
spheroidal  mass  of  vapors  circulating  around  the  sun 
with  a  rotation  in  the  same  direction  as  its  revolution. 
The  latter  case  has  been  the  more  common,  but  the  solar 
system  presents  us  the  first  case  in  the  four  small  planets* 
which  move  between  Jupiter  and  Mars." 

The  author  then  traces  the  same  process  in  the  history 
of  these  planetary  globes  of  fire  mist.  "The  regular  dis- 
ti-ibution  of  the  mass  of  the  rings  of  Saturn  around  his 
centre  and  in  the  plane  of  his  equator,  results  naturally 
from  this  hypothesis,  and  without  it  would  be  inexpli- 
cable. These  rings  appear  to  me  to  be  proofs  ever-exist- 

*  All  the  asteroids  then  known. 


HYPOTHESIS  OF  GENESIS   OF  SOLAR  SYSTEM.        615 

ing  of  the  primitive  extension  of  Saturn's  atmosphere 
and  its  successive  retreats."  Thus  the  remarkable  uni- 
formities in  planetary  conditions  and  movements  "flow 
from  the  hypothesis  which  we  offer,  and  give  it  a  strong 
probability  of  truth." 

The  diverse  inclinations  and  eccentricities  of  the  plan- 
etary orbits  are  attributed  to  the  "numberless  variations 
which  must  have  existed  in  the  temperature  and  density  ' 
of  the  different  parts  of  the  large  masses." 

4.  Relations  of   Comets  and  Zodiacal  Light. —  "In 
our  hypothesis,"  the  author  concludes,  "the  comets  are 
strangers  to  the  planetary  system."*     The   great   eccen- 
tricity of  their  orbits,  as  well  as  their  various  inclinations, 
is  a  consequence  of  the  present  hypothesis.       "  The  at- 
traction of  the  planets,  and  perhaps  also  the  resistance 
of  the  ethereal  medium  must  have  changed  many  comet- 
ary  orbits  into  ellipses   whose   longer  axis  is  much   less 
than  the  radius  of  the  sun's  activity."     "If  any  comets 
penetrated  the  atmospheres  of  the  sun  and  planets  during 
the  time  of  their  formation,  the  former  must  have  been 
precipitated   in   spiral   paths  upon   these   bodies,   and   by 
their  fall  have  displaced  the  planes  of  the  orbit  and  of  the 
equators    of    the    planets    from    the   plane    of    the    solar 
equator." 

"  If,  in  the  zone  abandoned  by  the  atmosphere  of  the 
sun,  there  existed  molecules  too  volatile  to  be  united 
among  themselves  or  with  the  planets,  they  must  have 
continued  to  circulate  about  the  sun  under  an  aspect  such 
as  the  zodiacal  light  presents,  but  with  too  great  tenuity 
to  oppose  any  sensible  resistance  to  the  various  bodies  of 
the  planetary  system,  a  result  which  would  also  flow  from 
a  motion  in  the  same  direction  as  that  of  the  planets." 

5.  Lunar  Synchronistic  Motions. — "A  profound  ex- 
amination of  all  the  circumstances  of  this  system  increases 

*  See  the  full  passage  quoted  above,  p.  182. 


616  LAPLACE'S  SYSTEM  OF  THE  WOELD. 

still  farther  the  probability  of  our  hypothesis.  The  primi- 
tive fluidity  of  the  planets  is  clearly  indicated  by  the 
flattening  of  their  figure."  The  vicissitudes  of  geological 
history  and  the  nature  of  the  succession  of  animals  and 
plants  upon  the  earth,  similarly  testify  to  a  progressive 
reduction  of  temperature. 

"  One  of  the  most  singular  phenomena  of  the  solar  sys- 
tem is  the  rigorous  equality  observed  between  the  an- 
gular motions  of  rotation  and  the  orbital  revolutions  of 
the  several  satellites.  The  probability  is  as  infinity  to 
one  that  this  is  not  the  result  of  chance.  The  theory  of 
universal  gravitation  causes  this  improbability  to  disap- 
pear by  showing  that  it  suffices  for  the  existence  of  this 
phenomenon  that  in  the  beginning  these  movements  should 
have  been  but  slightly  different.  At  that  time  the  at- 
traction of  the  planet  established  between  them  a  perfect 
equality,  but  at  the  same  time,  it  gave  birth  to  a  periodic 
oscillation  of  the  axis  of  the  satellite  directed  toward  the 
planet.  The  extent  of  this  oscillation  would  depend  on 
the  primitive  difference  of  the  two  movements.  The  ob- 
servations of  Mayer  on  the  libration  of  the  moon,  and 
those  which  MM.  Bouvard  and  Nicollet  have  made  on  this 
subject  at  my  request,  not  having  led  to  the  discovery  of 
such  an  oscillation,  the  difference  on  which  it  depends 
must  have  been  very  small.  This  circumstance  indicates 
with  extreme  probability  a  special  cause  which  originally 
embraced  this  difference  within  very  narrow  limits  where 
the  attraction  of  the  planet  has  been  able  to  establish 
between  the  mean  motions  of  rotation  and  revolution  a 
rigorous  equality,  and  has  subsequently  acted  until  it  de- 
stroyed the  oscillation  to  which  this  equality  had  given 
origin.  Both  these  effects  result  from  our  hypothesis,  for 
we  conceive  that  the  moon  in  the  state  of  vapor,  assumed 
through  the  powerful  attraction  of  the  earth,  the  form  of 
an  elongated  spheroid  whose  longer  axis  was  directed  con- 


HYPOTHESIS    OF    GENESIS    OP   SOLAR   SYSTEM.        617 

stantly  toward  this  planet.  This  would  result  from  the 
readiness  with  which  vapors  yield  to  the  feeblest  forces 
acting  upon  them.  Terrestrial  attraction  continuing  to 
act  in  the  same  manner  as  long  as  the  moon  was  in  a  fluid 
state,  must  at  length  by  continually  approximating  the 
periods  of  the  two  motions  of  this  satellite,  have  caused 
their  difference  to  fall  within  the  limits  where  their  rigor- 
ous equality  began  to  be  established.  Subsequently,  this 
attraction  must  have  destroyed,  little  by  little,  the  oscilla- 
tion which  this  inequality  produced  in  the  longer  axis  of 
the  spheroid  directed  toward  the  earth.  In  the  same  way, 
the  fluids  which  cover  this  planet  have  destroyed  by  their 
friction  and  by  their  resistance  the  primitive  oscillations 
of  its  axis  of  rotation  ;  for  this  is  now  subjected  only  to 
the  nutation  resulting  from  the  actions  of  the  sun  and 
moon." 

The  well  known  remarkable  relation  between  the 
orbital  motions  of  Jupiter's  satellites  is  explained  on  the 
nebular  hypothesis  in  a  manner  precisely  similar. 


CHAPTEE  Y. 

SYSTEMATIC    RESUME   OF   OPINIONS. 

r~MHE  foregoing  sketch  of  opinions  shows  that 
-*•  1.  Tho  two  fundamental  conceptions  of  nebular 
cosmogony  have  been  in  existence  ever  since  the  dawn  of 
Greek  philosophy.  These  are  :  (1)  The  conception  of 
widely  extended,  unorganized,  homogeneous  matter,  which 
the  Greeks  called  Chaos,  and  most  late  writers  have  iden- 
tified with  the  nebular  condition  of  matter  ;  (2)  A  vorti- 
cal movement  as  the  occasion  and  cause  of  the  differ- 
entiations of  atoms  and  parts,  and  the  organization  of 
structural  order. 

2.  The  theory  as  here  accepted  is  most    nearly  that 
which  was  promulgated  by  Laplace  ;  but  it  contains  prob- 
ably a  greater  amount  of  matter  which  was  original  with 
Kant. 

3.  The  modern  theory  was  impossible  until  Newton 
had    demonstrated  the   principle  of   universal  attraction, 
and    Newton    and    the    brilliant    mathematicians    of    the 
eighteenth  century  had  settled  analytically  the  dynamical 
principles  of  the  solar  system,  and  Sir  William  Herschel 
had  given  the  world  some  adequate  knowledge  of  nebular 
and  firmamental  relations.     Nor  was  the  modern  theory 
possible  until   the  mechanical  doctrine  of  heat,  and  the 
general  doctrine  of  the  conservation  of  energy,  and  the 
kinetic  theory  of  gases  had  been  firmly  established.     A 
whole  constellation  of    original   thinkers    have    therefore 
brought  their  respective  contributions  to   the  perfection 
and  confirmation  of  the   generally   accepted    doctrine   of 
cosmogenesis. 


VORTICAL   MOTION.  619 

The  part  which  the  several  cosmogonic  systems  and 
conceptions  contributed  to  the  modern  theory  may  per- 
haps be  most  intelligibly  set  forth  in  an  enumeration  of 
the  constitutive  principles  of  general  nebular  cosmogony. 

1.     A  HOMOGENEOUS  MEDIUM. 

Chaos.     1.    A   Continuous  substance.     Anaxagoras  (Homoeomeria) 
Descartes.     Compare  the  "primitive  fluid"  of  Sir  W.  Thomson. 

2.  An  Atomic  medium.     Leucippus,  Democritus,  Epicurus,  Lu- 
cretius and  other  Greek  atomists.    Newton  and  most  moderns. 
Compare  the  "monads"  of  Leibnitz. 

3.  Dynamical  molecules.     Boscovich,  ?  Faraday.      Compare  the 
"  vortical  atoms  "  of  Sir  W.  Thomson. 

Solar  emanation.     Kepler.     But  the  sun  and  planets  are  supposed 

already  existent. 

Plenum  of  matter  becoming  differentiated  into  Particles.     Descartes. 
Ethereal  Fluid.     Leibnitz.     But  the  planets  already  assumed  to  be 

in  existence. 

An  infinitude  of  Atomic  Vortices.     Swedenborg. 
Primitive  fluid  formed  of  all  the  matter  of  the  solar  system  dissolved 

into  its  elements.     Kant. 
Nebulous  Matter  existing  in  finite  regions  of  space.     Huygens,  Sir 

William  Herschel,  Laplace. 
Disappearance  of  the  medium  on  Formation  of  Planets.     Kant, 

Laplace. 

2.     VORTICAL  MOTION. 

Revolution  of  the  Heavens.     Egyptians,  Chaldaeans  and  Greeks. 
Rotation  of  the  Earth.     Hicetas,  Ecphantus,  Heraclides,  Cusanus. 
Revolution  of  the  Earth.    Aristarchus,  Seleucus,  Archimedes,  Arya- 

batta,  Copernicus. 
Elemental ,  Vortices.     1.  Inaugurated  by   The  Mind.     Anaxagoras. 

Torricelli,  Galileo,  Descartes,  Swedenborg.     Compare  "  Vortical 

Atoms"  by  Sir  William  Thomson. 

2.  Existing  from  eternity.     Leucippus,  Democritus. 

3.  Originated  by  self  determination.     Epicurus,  Lucretius,  Gas- 
sendi,  Leibnitz,  Rosmini,  Campanella. 

Systemic  Vortices.     1.  One  Solar  Vortex.     Kepler. 
2.   Planetary  and  Solar  Vortices. 

(a.)  Origin  not  explained  on  Mechanical  Principles.     Descar- 
tes, Leibnitz,  Swedenborg,  Wright,  Lambert. 


620  SYSTEMATIC    RESUME   OF    OPINIONS. 

(b.)    The  result  of  mechanical  action.    Kant,  Laplace  (except 

solar  rotation). 

Nebular  Vortices.     Kant,  Herschel,  Laplace. 
[Firmamental  Rotation.     Wright,  Kant,  Lambert.] 
Orbital  Movement  of  Our  Sun  in  Space.     Laplace.  Herschel  (not 
stated  to  be  orbital). 

3.     UNIVERSAL  CONCURRENCE  OF  MATTER. 

Love,  with  its  antithesis,  Hate.     Empedocles. 

Cosmical  Magnetism.     Kepler  (who  utilized  attraction  and  repul- 
sion), Swedenborg. 

Universal  Attraction.     Newton,  Wright,  Kant,  Lambert,  Herschel, 
Laplace. 

Pressure  and  Impulse.      1.    From  a  cosmical  fluid.      Descartes, 
Leibnitz. 
2.   Storm  of  "  ultramundane  corpuscles."    Le  Sage.* 

Consequent  central   Condensation.     Kant  (except  at   the  centre), 
Herschel  (in  nebulae). 

Consequent  Heat  and  Luminosity.     Lichtenberg,  Kant. 

4.     THERMAL  RADIATION  AND  CONTRACTION. 

Condensation  around  Solar  and  Planetary  Centres.  Kant,  Laplace. 
Heat  and  Luminosity  maintained.     Helmholtz,  etc. 

5.     ANNULATION. 

One  Equatorial  Ring  accumulated.     Swedenborg. 
Saturnian  Ring  thrown  off  (possibly  other  planetary  rings).     Kant. 
Successive  Solar  Equatorial  Rings  abandoned.     Laplace. 
Stratification  of  Rings.     Kant  (in  respect  to  Saturn's),  Laplace. 
Saturnian  Rings  but  Swarms  of  small  Satellites.     Cassini,  Kant, 

Peirce,  Clerk-Maxwell. 

Tfie  Zodiacal  Light  a  similar  Ring.     Kant,  Laplace. 
Annulation  in  existing  Nebula:.     Herschel. 

6.    SPHERATION  OF  RINGS. 
One  Ring  disrupted  formed  the  Several  Planets,  which  were  thrown 

outward  to  their  respective  positions.     Swedenborg. 
Each  of  Several  Rings  gathered  into  a  planetary  mass.     Laplace. 

*  Le  Sage :  Lucrece  Newtonien :  Traite  de  Physique  Mecanique,  Geneva,  1818. 
See  also  Constitution  de  la  Matiere,  etc.,  par  le  P.  Leray.  Paris,  1869,  and  Tail's 
Recent  Advances  in  Physical  Science,  299. 


CYCLES   OF   COSMIC    EXISTENCE.  621 

In  one  instance  a  ring  resulted  in  Numerous  Asteroids.     Laplace. 
The  Asteroids  may  have  resulted  from  a  Stratified  Ring. 

7.     EFFECTS  OF  PERTURBATIVE  ATTRACTIONS. 
Inclinations  of  Planetary  Axes.     Kant,  Laplace  (who  also  appeals  to 

cometary  precipitation). 
Eccentricities  of  Orbits.    Laplace. 

8.  DISLOCATIONS  OF  PLANETARY  CRUSTS. 
Orographic  Inequalities  caused  by  confined  gases.     Leibnitz,  Kant. 

9.  GENERALIZATION  OF  COSMIC  HISTORY. 
Successive  Stages  of  Star  and  Planet  formation  from  a  nebula  —  a 

planet  a  cooled  sun.     Leibnitz,  Kant,  Herschel,  Laplace. 

Jupiter  in  an  early  stage  of  development.     Kant. 

The  Moon  in  a  fossilized  condition.     Frankland.* 

Other  planets  habitable,  or  destined  to  be  so.  Kant,  Lambert,  Her- 
schel, Laplace. 

The  various  Colors  of  the  Stars  indicative  of  successive  Stages. 
Laplace,  Secchi.1: 

10.     CYCLES  OF  COSMIC  EXISTENCE. 

Decay  of  Worlds  in  one  region  compensated  by  New  Organisms  in 

another.     Kant,  Herschel. 

Occasional  Revival  of  waning  suns.     Kant,  Herschel. 
Resuscitation  of  Cosmic  Organisms  by  Precipitation  and  Impact. 

Kant. 

*Proc.  Roy.  Inst.,  iv,  175.  The  idea  was  advanced  in  the  present  writer's 
Sketches  of  Creation,  in  March,  1870.  Compare  L.  Ssemann:  On  the  Unity  of 
Geological  Phenomena  in  the  Solar  System,  Bull,  de  la  Soc.  geol.  de  France,  4 
Feb.,  1861;  J.  Nasmyth:  On  the  Age  of  the  Moon's  Surface,  Proc.  Manchester 
Lit.  and  Phil.  Soc.,  Nov.  15, 1864. 

tSecchi:  Le  Soleil. 


INDEX. 


Abney  on  matter  in  space,  58,  61, 
64,  "481. 

Absorption  of  fluids,  383;  on 
moon,  402,  407 ;  on  Jovian  sat- 
ellites, 441;  on  planets,  460; 
index  of,  460;  on  the  earth, 
467-9 ;  on  Mars,  Asteroids  and 
Jupiter,  472;  on  Venus  and 
Mercury,  473. 

Acceleration,  rotary,  from  shrink- 
age, 459;  from  tidal  action, 
251. 

Acceleration  of  tide-producer 
240. 

Adams,  J.  C.,  on  meteoric  orbits, 
17;  on  moon's  acceleration,  474. 

Adhemar,  on  effect  of  precession, 
288. 

Aeriform  agents  in  mountain 
making,  292,  324. 

Age,  of  moon,  379;  of  Mars,  415 
-6,  470;  of  Jupiter,  427,  429; 
of  Saturn,  443 ;  of  Uranus  and 
Neptune,  444-8. 

Age  of  the  world,  alleged  too 
great,  179-81;  calculations  on, 
355,  470;  table  of,  365. 

Ages  of  planets  in  a  system,  215, 
216,  415. 

Aggregation  of  costnical  matter, 
66,  71,  92,  185-6;  heat  arising 
from,  92-4. 

Airy,  Gr.  B.,  on  tides,  225;  on 
change  of  axis,  334;  quoted, 
330. 

Alcyone  as  fancied  centre  of  fir- 
mament, 140. 

Alexander,  Stephen,  on  zodiacal 
light,  25;  on  clusters  and 


nebulas,  146;  on  consistencies 
of  nebular  cosmogony,  150. 

Alps,  fan  structure  in,  308,  309. 

Amorphous  nebulas,  42. 

Anaxagoras,  on  upheavals,  292; 
on  first  principle,  552. 

Andrews,  E.,  on  geological  time, 
374. 

Angstrom  on  zodiacal  light,  24. 

Annular  nebula?,  45,  46. 

Annulation  of  nebulae,  106-19; 
involving  entire  nebula?,  117; 
alleged  improbable,  186;  con- 
ditions of,  188-9;  according  to 
Faye's  speculation,  203,  209; 
denied  by  Spiller,  212;  concep- 
tion of  in  cosmogony,  613,  620. 
See  "Ring." 

Anticipation  of  tide,  234. 

Anti-tide  denned,  224;  acting  on 
rotation,  237;  acting  on  incli- 
nation of  axis,  245. 

Appalachian  region,  315. 

Apsides,  motion  of,  285, 

Arago,  P.,  on  meteors,  7,  14,  16; 
on  nebular  changes,  92;  on 
astronomical  climates,  296; 
cited,  146. 

Archibald,  E.  D.,  on  Siemens' 
theory,  57. 

Archimedes  cited,  551. 

Aristarchus  cited,  551. 

Aristotle  on  figure  of  earth,  552. 

Aryabatta  cited,  552. 

Asteroidal  mass,  disrupted  state 
of,  an  alleged  difficulty,  176. 

Asteroids  a  sort  of  meteoric  ring, 
35 ;  mass  of,  alleged  too  small, 
175;  origin  of,  in  a  stratified 
ring,  176;  or  from  an  intra-Jo- 
vian  ring,  177,  614. 


624 


INDEX. 


Astronomical  changes  and  plane- 
tary conditions,  278. 

Atkinson,  A.  S.,  on  comet  of 
1882  b,  31. 

Atmosphere,  effects  of  low  den- 
sity of,  271,  504;  of  moon  ab- 
sorbed, 382,  407 ;  homogeneous, 
411;  of  Mars,  504;  of  sun,  612. 

Atmospheric  factor  on  moon,  410; 
feebleness  of,  410  seq. ;  deduc- 
tions from,  412;  on  Mars,  419; 
on  Venus,  420;  on  Mercury, 
423;  on  Jupiter,  428,430. 

August  meteors,  19,  20,  33. 

Axes  of  planets,  inclinations  of, 
129 ;  increased  by  lagging  tides, 
243. 

Axis,  change  of  position  of,  334. 

B 

Babbage,  C.,  on  isothermal  lines 
in  crust,  275,  332. 

Bache,  A.  D.,  on  ocean  bottom, 
302. 

Backlund  on  Encke's  comet,  480. 

Bakewell,  R.,  on  Niagara  gorge, 
369. 

Ball,  R.  S.,  on  primitive  terres- 
trial tides,  263. 

Baltzer  on  slipping  of  crust,  311. 

Bar  of  Mississippi  River,  453. 

Barnard,  E.  E.,  cited,  5;  on 
comet  of  1862  b,  30. 

Barnard,  P.  A.  P.,  on  zodiacal 
light,  25. 

Barnard,  G.  J.,  on  tides,  225;  on 
Mallet's  theory,  319,  347;  on 
terrestrial  rigidity,  341. 

Barometer,  height  of  on  moon, 
411. 

Barrande,  J.,  on  colonies,  281. 

Bartlett,  J.  R.,  on  ocean  bottom, 
302. 

Beaumont,  E.  de,  on  a  wrinkling 
crust,  295;  on  terrestrial  cool- 
ing 296;  on  earth's  age,  356. 

Beche,  de  la,  on  rock  absorption, 
461. 

Beer  and  Maedler  on  moon,  385. 

Belt,  T.,  on  glaciation,  285;  on 
Niagara  gorge,  370. 


Bentley  on  habitability,  497. 

Bergeron  cited,  408. 

Bernouilli,  D.,  on  tides,  225. 

Bernouilli,  John,  cited,  565. 

Berthelot  on  dissociation  of  mat- 
ter, 48. 

Bessey,  C.  E.,  on  yellow  rain,  7. 

Biela's  comet,  32,  34. 

Biot  on  zodiacal  light,  26. 

Bischof  on  age  of  the  earth,  179; 
on  elastic  force  of  steam,  294; 
on  rock  absorption,  464. 

Bluff  recession,  rate  of,  374,  378. 

Bode,  J.  E.,  cited,  598. 

Boiling  point  on  moon,  412. 

Bond,  G.,  on  nebula?,  42. 

Bore,  tidal,  400. 

Boscovich  on  atoms,  569. 

Boss  L.,  on  lunar  maps,  385. 

Boucheporn  on  collision  with 
comets,  334. 

Bredechin  on  tails  of  comets,  78. 

British  Association  on  meteoric 
dust,  11. 

Brodie,  B.,  on  constitution  of 
matter,  49,  54. 

Bruno,  Giordano,  cited,  496,  553. 

Buckingham    on    crater    Linne, 

QQO 
uW« 

Buffon  cited,  339 ;  hypothesis  of, 

611. 
Burnham,  S.  W.,  on  double  stars, 

512,  513. 
Byrgius  crater,  390. 


Callaway,  C.,  on  primitive  tides, 
265. 

Calvert  on  meteoric  dust,  13. 

Campanella  cited,  558. 

Capellar  phase,  541. 

Carnelly,  T.  on  water  under  pres- 
sure, 270. 

Carpenter,  W.  B.,  on  area  of 
ocean,  466. 

Cassini  on  zodiacal  light,  24;  on 
Mercury,  423;  on  Saturn's 
rings,  582. 

Central  solidification,  220. 

Centrifugal  force  in  ring  making, 
110,  115;  in  tides,  129;  in  ar- 


INDEX. 


625 


rangement  of  heavier  matters, 
137. 

Centripetal  influence  in  tides, 
129;  in  arrangement  of  heavier 
matters,  137. 

Chandler,  S.,  on  comet  of  1882  b, 
31. 

Chaotic  stage,  539,  618,  619. 

Chemical  reactions  on  primeval 
planets,  274,  327. 

Childrey  on  zodiacal  light,  26 

Chladni  on  meteors,  13,  16. 

Clark,  Alvan,  on  companion  of 
Sirius,  434. 

Clarke,  F.  W.,  on  constitution  of 
matter,  49,  56. 

Clausius,  R.,  on  freezing  under- 
pressure, 27;  on  reconcentra- 
tion  of  energy,  493. 

Clefts  on  moon",   391. 

Climates,  deterioration  of.  485; 
cause  of,  486. 

Climatic  forces,  in  early  times, 
269 ;  resulting  from  astronomi- 
cal changes,  278-90:  affected 
by  increased  obliquity,  283 ;  by 
motion  of  apsides,  285;  by 
changes  in  eccentricity,  298. 

Clissold  on  Swedenborg,  566. 

Cloudiness  on  Venus,  422;  on 
Mercury,  424;  on  Jupiter,  433, 
434,  435;  on  ultra-Jovian  plan- 
ets, 447. 

Clouds,  first  formation  of,  272. 

Clusters  of  stars,  47,  48 :  in  Her- 
cules, 118. 

Coagulating  nebula,  105. 

Collision  of  worlds,  478,  516,  518. 

Colonies  in  palaeontology,  281. 

Colors  of  stars,  522  seq.~,  528. 

Comet  of  1881,  29. 

Comet  of  1882  b,  30,  disintegra- 
tion of,  31. 

Comets,  motions  and  phenomena 
of,  27 ;  of  short  period,  28 : 
tenuity  of,  32,  184;  disintegra- 
tion of,  31,  32,  75,  206,  482; 
connected  with  meteoric  show- 
ers, 32,  33,  34,  75;  physical 
condition  of,  34,  40 ;  tails  of,  as 
viewed  by  Newton,  51;  evolu- 


tion of,  73;  determination  of 
orbits  of,  73-4;  influenced  by 
planets,  74;  light  of,  77;  tail's 
of,  77-8;  as  strangers  in  our 
system,  182,  196,  610,  615;  di- 
rection of  motion  of,  182;  con- 
trolled by  same  laws  as  planets, 
183;  origin  of  on  Paye's  the- 
ory, 205,  211. 

Common,  A.  on  comet  of  1882  b,  31. 

Comparative  geology,  the  keys  of, 
534. 

Composition  of  fixed  stars,  191. 

Conception,  final,  of  orogenic 
history,  326-31. 

Conceptions  respecting  mountain 
making,  323. 

Conspectus  of  views  on  matter  in 
space,  65 ;  on  orogenic  specula- 
tions, 331. 

Continental  trends,  352. 

Contractional  theory  in  orog- 
raphy, 294-314,  324;  inade- 
quacy of,  314. 

Contraction  as  a  source  of  heat, 
81-7;  as  cause  of  acceleration, 
459. 

Cooling  of  planets,  458. 

Cooling  planet,  conditions  on,  215. 

Cooling  through  descent  of  rains, 
273 ;  impeded  by  crust,  275. 

Cope  on  habitability,  498. 

Copernicus  crater,  387;  radial 
streaks  of,  390,  404. 

Cornelius,  C.  S.,  on  nebular  evo- 
lution, 120. 

Cosmical  dust,  examples  of,  3; 
citations  on,  11 ;  quantity  of,  13 ; 
general  view  on,  48;  sundry 
opinions  on,  49-65;  aggrega- 
tion of,  66,  71 ;  resisting  action 
of,  69-71;  primordiality  of, 
539.  See  also  "  matter  of 
space." 

Cosmical  speculation,  65. 

Cosmic  history  generalized,  621, 

Cosmic  periods,  215,  216,  450;  on 
moon,  380;  on  Mars,  415;  on 
Jupiter,  429;  on  Jovian  satel- 
lites, 438 :  on  ultra-Jovian  plan- 
ets, 445. 


INDEX. 


Cosmic  tides  influencing  rotation, 
129. 

Cosmogony.  See  "  Nebulae," 
"  Cosmical  dust,"  "  Tides," etc. 

Craters,  lunar,  386,  390;  Coper- 
nicus, 387;  Theophilus,  map  of, 
388;  Tycho,  389;  Kepler  and 
others,  390;  floors  of ,  408. 

Croll,  J.,  on  nebular  heat,  93,  207: 
on  age  of  the  sun,  179;  on  cli- 
matic effect  of  precession,  288; 
on  influence  of  eccentricity, 
289;  on  change  of  axis,  334;  on 
geological  time,  368,  373;  on 
continental  erosion,  373,  374. 

Crookes,  W.,  on  radiant  matter, 
49.  77. 

Cruls  on  comet  of  1882  b,  30. 

Crushing  influence  of  tides,  131, 
255,  347. 

Crushing,  thermal  effects  of,  131, 
255,  346,  347. 

Crust,  incipient,  218:  slipping  of, 
220,  308-9;  transformations  of, 
274-8;  fire-formed,  274;  influ- 
ence of  in  cooling,  275;  sink- 
ing as  formed,  307;  subsidence 
of,  314-9 ;  unequal  thickness  of, 
335 ;  thicker  under  the  oceans, 
337;  on  moon,  402;  of  ice,  442, 
446. 

Currents  on  the  surface  of  a  neb- 
ula, 130. 

Cusanus  cited,  552. 

Cutting,  H.  A.,  on  rock  absorp- 
tion, 462. 

Cuvier,  G.,  on  Leibnitz,  558. 

Cycle,  cosmic,  534-48,  621 ;  reflec- 
tions on,  544. 

Cycles  of  matter,  495. 


Dana,  J.  D.,  on  influence  of 
ocean  in  wrinkling,  301;  on 
mountain  making,  302,  303;  on 
subsidence  of  cnist,  316;  on 
synclinorium,  322;  on  trends  in 
Pacific,  352;  on  time  ratios, 
358,  364. 

Darwin,  C.,  on  age  of  the  earth, 
180. 


Darwin,  G.  H.,  cited,  581;  on 
retral  sliding  of  tide,  235;  on 
submeridionality,  255 ;  memoirs 
by,  258;  on  primitive  tides, 
265;  on  velocity  of  wind,  269; 
on  terrestrial  cooling,  296;  on 
change  of  axis,  334;  on  earth's 
rigidity,  343. 

Daubeney  on  mountain  making, 
293;  on  earth's  interior,  339. 

Daubree  on  meteoric  dust,  8,  11. 

Davy,  H.,  on  mountain  making, 
293,  332;  on  the  earth's  interi- 
or, 339. 

Dawson,  J.  W.,  on  slipping  of 
crust,  309. 

Decay,  planetary,  451;  according 
to  Kant,  585. 

Deep-sea  temperature,  337. 

Deformative  tide,  226;  crushing 
influence  of,  255. 

Delambre,  cited,  551. 

Delaunay  on  terrestrial  rigidity, 
341;  on  tidal  retardation,  474. 

Delesse  on  rock  absorption,  464. 

Delta  of  Mississippi  River,  372, 
453. 

Democritus  cited,  553. 

Denuing,  W.,  on  meteorites,  13. 

Densities  of  Jovian  satellites, 
440;  of  planets,  579. 

Densities  of  outer  planets  alleged 
too  low,  177. 

Density  of  Saturn,  443;  Uranus 
and  Neptune,  443;  Jovian  sat- 
ellites, 440. 

Density  of  atmosphere,  effects  of 
low,  271. 

Density  of  solar  nebula,  161-4, 
421,  424,  589;  fallacy  concern- 
ing, 178;  influence  of  on  or- 
bital velocity,  161 ;  alleged  too 
low,  184. 

Density  under  mountains.  322, 
330. 

Deposition  and  time,  369. 

Derham,  W.,  cited,  496. 

Dosrurtes  on  a  wrinkling  crust. 
295;  on  earth's  interior,  339; 
vortical  theory  of,  554. 

Deschanel  cited,  412. 


ItfDEX. 


627 


Desiccation  of  continents,  471. 

Desor,  E.,  on  Niagara  gorge,  369. 

Deville  on  dissociation  of  matter, 
48;  on  rock  absorption,  464, 

Dewar  on  Lockyer's  views,  49. 

Direct  rotation,  how  resulting, 
123-4. 

Direction  of  rotation  in  resulting 
spheroid,  123-9;  what  it  de- 
pends on,  123;  how  estimated 
by  Paye,  203. 

Discoid  ring,  111-2. 

Discordant  tides,  239;  action  of 
on  rotation,  398,  404. 

Disintegration  of  comets,  31,  32, 
75,  206,  482 ;  of  Saturn's  rings, 
483. 

Disruption  of  a  nebular  ring,  119, 
208. 

Dissipation  of  energy,  489. 

Dissociation  of  matter,  opinions 
on,  48:  in  space,  59;  in  the 
sun,  59;  in  nebulae,  193. 

Distances  of  planets  in  Faye's 
theory,  205. 

Distortion  from  tides,  439. 

Divination,  scientific,  535. 

Doberck,  W.,  on  comet  of  1882 
b,  30. 

Donatf  s  comet,  47. 

Doolittle,  M.  H.,  on  resisting 
matter  in  space,  70. 

Downthrow  of  strata.  304. 

Draper,  J.  W.,  on  red  heat,  272; 
on  spectrum  of  Orion  nebula, 
531. 

Drayson  on  glaciation,  285,  290. 

Dufour  on  meteoric  matter,  14. 

Dumas  on  dissociation  of  matter, 
48. 

Duncan,  P.  M.,  on  solar  heat,  56. 

Du  Prel  on  discoid  ring,  112. 

Durocher  on  rock  absorption,  461. 

Dust  fall*,  6. 

Dust  of  time,  3. 

Dust,  organic,  6.  7. 

Dust,  volcanic,  7. 

Dutton,  C.  E.,  on  contraetional 
theory,  304-7:  on  internal  tem- 
peratures, 306;  on  slipping  of 
crust,  308. 


Dykes  on  moon,  403. 
Dynamical  theory  of  tides,  225. 


Earth,  tidal  influence  of,  248; 
planetologically  viewed,  338 
seq. ;  former  high  temperature 
of,  339;  present  interior  of, 
339;  rigidity  of,  340;  meridion- 
al trends  on,  350;  age  of.  355; 
a  former  sun,  380. 

Earthquakes  connected  with 
moon,  348. 

Eastman,  J.  R.,  on  meteors,  5. 

Eccentricity  of  planetary  orbits, 
174;  climatic  influence  of,  288- 
90;  Kant's  theory  of,  580. 

Ehrenberg  on  meteoric  dust,  6. 
13. 

Elastic  forces  in  a  contracting 
body,  84. 

Electricity  on  primeval  planet, 
273. 

Elemental  atoms,  49. 

Elements,  compound  nature  of, 
48. 

Elevation  without  plication,  304. 

Elliptic  orbit,  how  caused,  67,  74, 
174,  554,  556,  564,  576,  615. 

Elliptic  orbits  alleged  unexplain- 
ed, 173. 

Empedocles  on  love  and  hate,  553. 

Encke's  comet  resisted,  479. 

Endlich,  F.  M.,  on  explosive  phe- 
nomena, 339;  on  desiccation, 
471. 

Ennis,  J.,  on  spiral  nebulae,  99; 
on  rotation  of  nebulae,  165: 
cited,  339. 

Eozoic  tides,  265. 

Epicurus  cited,  553. 

Equal  areas,  law  of,  106,  613 ;  in. 
fluence  of  in  direction  of  rota- 
tion. 124. 

Equatorial  lands  more  or  less 
emergent,  278. 

Equilibrium,  final,  in  nature,  488 
seq, 

Equilibrium  theory  of  tides,  225. 

Equinoxes,  motion  of,  285. 

Eroded  condition  of  planets,  451. 


628 


INDEX. 


Erosion  along  anticlinals,  335. 

Erosion,  amount  of,  451;  at  Ni- 
agara gorge,  3G9,  378,  452;  in 
remote  times,  452;  of  Missis- 
sippi, 372,  378,  453 ;  on  Mercury 
and  Venus,  457;  on  moon,  457; 
on  Mars,  458 ;  on  Jovian  satel- 
lites, 458. 

Erosion  and  time,  369,  374. 

Erosion  limited  on  moon,  412. 

Erosive  action,  of  tides,  268:  of 
lava  torrents,  399. 

Eruption  on  temporary  star,  517. 

Eruptive  phase,  543. 

Eta  Argus,  changes  on,  88. 

Ether,  Newton's  views  on.  50-2; 
influence  of.  479. 

Evolution,  tidal.  See  "Tides," 
etc. 

F 

Falcate  forms  of  nebulas,  102-3. 

Fan  action  about  the  sun,  59,  60. 

Fan  structure  in  the  Alps,  308, 
309. 

Faunal  changes  and  astronomical 
conditions,  281,  284. 

Favre,  A.,  on  a  wrinkling  crust, 
297. 

Faye,  on  Siemens'  solar  theory. 
61 ;  on  tails  of  comets,  78 ;  on 
direction  of  rotation,  128;  on 
retrograde  motions,  153,  158; 
on  periodic  time  of  Phobos,  168; 
on  comets  belonging  to  our 
system,  182;  on  improbability 
of  annulation,  187;  this  opin- 
ion examined,  189-90;  on  a 
modified  form  of  nebular  theory 
198-207;  criticisms  of,  207-14; 
on  subsidence  of  ocean's  bot- 
tom, 317,  328,  332;  on  geal 
tide  on  moon,  384;  on  lunar 
geology,  407;  on  lunar  fluids, 
471;  oh  solar  spots.  ."»20. 

Ferrel.  W.,  on  tides.  225. 

Film  tide.  227. 

Final  causes,  608. 

Finiteness  of  the  world,  491,  505. 

Finlay,  on  comet  of  1882  b,  30. 

Fire-formed  crust,  274;  disap- 
pearance of,  277, 


Fire-mist  stage  of  a  planet,  217; 
of  the  stars,  526,  530,  532;  of 
nebula3,  540. 

Firmamental  organization.  574, 
598,  602,  605. 

Fisher,  0.,  cited,  347;  on  earth 
oscillation,  260;  on  terrestrial 
cooling,  296;  on  radial  contrac- 
tion, 303;  on  contractional 
theory,  306;  on  terrestrial 
physics, 306;  on  internal  vapors, 
311;  on  mashing  together,  321 : 
on  roots  of  mountains.  321 ;  on 
orogeny,  334;  on  origin  of 
ocean's"  basin,  335;  on  internal 
solidity,  341;  on  earth's  age, 
356. 

Fisk,  J..  corrected,  503. 

Fixed  stars,  in  motion.  141,  575; 
alleged  not  uniform  in  compo- 
sition, 191. 

Flammarion  on  habitability,  496. 

Flight,  W.,  on  meteoric  occlu- 
sions, 58. 

Floating  mineral  matters,  218. 

Flood,  cause  of,  583. 

Flow  on  surface  of  nebula,  130. 

Fluctuation,  total,  of  a  tide, 
226-7. 

Fluids  on  moon,  402.  407. 

Folds  of  crust.    See  "  Wrinkles." 

Forbes,  I).,  on  Mallet's  theory, 
319. 

Forbes,  President,  on  habitabil- 
ity, 497. 

Forces  of  nature,  magnitude  of, 
223. 

Forms  of  nebula1  changing,  87-94 : 
causes  of,  99-104. 

Formula  for  law  of  angular  ve- 
locity, 109;  linear  velocity,  110; 
width  of  nebular  ring,  li6;  di- 
rection of  rotation,  126;  law  of 
density  in  the  solaj*  nebula 
(Faye),  128,  189,  204;  constancy 
of  differential  centrifugal  ten- 
dency, 138;  equal  differential 
centrifugal  and  centripetal  ten- 
dencies, 139 ;  relations  of  peri- 
odic times,  159,  167;  periodic 
time  n  times  as  great,  169 ;  con- 


INDEX. 


ditions  of  no  annulation,  188; 
relation  of  contraction  to  annu- 
lating  velocity,  190;  tenuity  of 
solar  nebula,  200;  orbital 
motion  in  a  hollow  sphere,  202; 
relative  length  of  planetary 
periods,  216;  efficiency  of  tidal 
force,  228;  linear  height  of 
tide  at  any  point,  228;  linear 
height  on  homogeneous  sphe- 
roid, 229 ;  linear  height  on  the 
earth,  229;  zero  tide,  229;  tide 
on  one  planet  in  terms  of  tide 
on  another,  229;  retardative 
component  of  tidal  force,  233; 
equatorial  centrifugal  force  on 
the  earth,  257 ;  erosive  efficiency 
of  tides,  268 ;  earth's  heat  as  a 
sun,  380;  absorption  of  water, 
382;  absorption  of  water  and 
air,  383;  geal  tide  on  moon, 
384;  density  of  atmosphere  on 
a  planet,  411 ;  determination  of 
altitude  by  barometer,  411; 
temperature  of  boiling  point, 
412;  height  of  tide  on  any 
planet,  with  any  tide-mover, 
418;  centrifugal  force  in  terms 
of  same  on  another  planet, 
426 ;  intensity  of  gravity  in  geal 
terms,  426;  various  Jovian  rela- 
tions to  earth,  427-8;  height  of 
homogeneous  atmosphere  on 
any  planet,  430;  height  of  earth's 
homogeneous  atmosphere, 
430-1 ;  moment  of  inertia  of  a 
sphere,  437;  final  levelling  of 
land,  456;  indices  of  rock  ab- 
sorption, 463-4;  specific  gravity 
of  rocks,  463-4;  atmospheric 
pressure  in  a  deep  shaft,  469. 

Fourier  on  a  problem  in  thermics, 
305. 

Fragmental  deposits  in  moun- 
tains, 318. 

Frankland  on  porosity  of  moon, 
465;  on  heat  of  Orion  nebula, 
532. 

Freezing  point  under  pressure, 
270. 

Friction  in  nebular  matter,  100, 


122,    124,    127,    165;    in  tides, 

233,  250.     See  "Tides." 
Frisby,  E.,  on  comet  of  1882  b, 

31. 
Furrows  the  counterpart  of  wrin- 

kles, 300. 

G 

Gardner,  J.  S.,  on  subsidence  of 

crust,  316,  334. 
Gardner,  J.  T.,  on  Xiagara  gorge, 

370. 

Gases  in  mountain  making,  292. 
Gassendi  cited,  553. 
Gautier  on  nebula?,  42,  88,  92. 
Geal  tides  on  moon,  248,  396  seq. 
Geanticlinals,  327. 
Geikie,    A.,    on  continental  ero- 

sion, 373. 

Geognostic  regions,  357. 
Geology,  pure,  536:  comparative, 

536-7. 
Geosynclinals,  deposition  along, 

314;  uplift  of,  318. 
Gilbert,  G.  K.,  on  lacolitic  moun- 

tains, 294. 
Gilmore,  Q.  A.,  on  rock  absorp- 

tion, 462. 

Glacial  periods  and  time,  368. 
Gordon-Gumming,  Miss  C.  F.,  on 

floating  lava,  218. 
Gorge  of  Niagara,  369  seq.  ;  of  St. 

Anthony,  372,  378. 
Gravity  on  moon,  400-1  ;  on  Mars. 

415;  on  Jupiter,  426. 
Green  on  internal  vapors,  311. 
Gregory  on  Kepler,  554  ;  on  Des- 

cartes, 555. 
Grenfel,  J.  G.,  on  primitive  tides, 

265. 

Groombridge  1830,  motion  of,  92. 
Grove,  W.  R.,  on  matter  in'space, 

52. 

Gruithuiseh  on  moon,  385. 
Guy,  H.  B.,  on  river  sediments, 


uppy 
373. 


Gyration,  radius  of,  in  planets, 
162,  437. 

H 

Haanel,   E.,   on   constitution  of 
elements,  48. 


630 


INDEX. 


Habitabilityof  other  worlds.  496: 
absolutely  viewed,  497-500; 
viewed  from  human  standard, 
500;  restricted  limits  of,  507; 
Kant  on,  591. 

Hall,  J.,  on  distribution  of  faunas, 
281;  on  central  heat,  295;  on 
sedimentation  along  geosyncli- 
nals,  314;  on  orogeny,  333;  on 


Niagara  gorge,  369. 

Hall,  James  (of  Edinburgh),  on  a 
wrinkling  crust,  295. 

Hall,  Maxwell,  on  solar  heat,  61. 

Halley  on  meteors,  16. 

Hannay,  J.  B.,  on  water  under 
pressure,  270. 

Harmonic  circulation,  564. 

Haughton,  S.,  on  primitive  tides, 
265;  on  change  of  axis,  334. 
580  ;  on  time  ratios,  359  ;  on 
geological  duration,  366;  on 
area  of  ocean,  466;  cited,  341. 

Hayden,  F.V.,  on  desiccation,  471. 

Heat  resulting  from  contraction, 
81-7;  from  tidal  crushing,  256; 
from  contractional  crushing, 
319-23;  in  the  stars,  526. 

Heavier  matters,  how  arranged, 
137. 

Heim,  A.,  on  contractional  theo- 
ry, 312. 

Helmholtz  on  matter  in  space,  52  ; 
on  solar  heat,  81;  on  nebular 
rotation,  94;  on  age  of  the  sun, 
179;  on  dissipation  of  energy, 
489  ;  on  vortex  ring,  569. 

Helvetius  on  lunar  surface,  385. 

Hennessey,  II.  G.,  cited,  341. 

Heraclides  cited,  551. 

Hercules,  cluster  in,  118;  solar 
motion  toward,  141,  202. 

Herschel,  A.  S.,  on  the  constitu- 
tion of  matter,  61,  533. 

Herschel,  J.,  on  Orion  nebula, 
105  ;  on  isothermal  lines  in 
crust,  278;  on  astronomical 
causes  of  climate,  290;  on  a 
plastic  zone,  315;  on  lunar  cra- 
ters, 387;  on  ratio  of  land  and 
water,  466;  on  mass  of  atmos- 
phere, 468;  on  nebulae,  598,  605. 


Herschel,  W.,  on  nebute,  35,  41 ; 
on  Magellanic  Clouds,  88;  on 
orders  of  nebulae,  140 ;  on  Mar- 
tial ice  caps,  416;  on  habita- 
bility  of  sun,  497;  on  structure 
of  the  heavens,  598;  cited,  146; 
511. 

Hicetas  on  rotation  of  earth,  551. 

Hilgard,  E.  W.,  cited,  372;  on 
crushing  effects,  347. 

Hilgard,  J.  E.,  on  Gulf  of  Mexi- 
co, 453. 

Hinrichs,  G.,  on  dissociation  of 
matter,  48;  on  spiral  nebulae, 
101;  on  direction  of  rotation, 
127;  on  planetary  velocities, 
159;  on  planetary  intervals. 
173. 

Hire,  de  la,  cited,  575. 

Him,  A.,  on  Siemens'  theory,  63, 
64;  on  Saturn's  rings,  483. 

Hirsch  on  geological  climates, 
290. 

Hitchcock,  C.  II.,  on  pressure 
from  continental  side,  309;  on 
mashing  together,  323 ;  on  mol- 
ten origin  of  granites,  517. 

Holden,  E.  S.,  on  changes  in 
nebulae,  88. 

Homogeneous  atmosphere,  430. 

Hopkins,  W.,  on  floating  rock 
masses,  218,  272;  on  a  wrink- 
ling crust,  296 ;  on  local  lakes 
of  lava,  332;  on  internal  li- 
quidity, 340,  346. 

Horizontal  component  of  tidal 
force,  232,  351. 

Hough,  G.  W.,  on  Jupiter,  429. 

Huggins,  W.,  on  nebular  spectra, 
47;  on  cometary  spectra,  58; 
on  motion  of  nebulae,  91;  on 
crater  Linne,  392;  on  tempo- 
rary star,  514;  on  spectrum  of 
Orion  nebula,  531. 

Humboldt,  A.,  cited,  5;  on  zodi- 
acal light,  23,  24;  on  matter  in 
space,  53;  on  temporary  stars, 
514;  on  Laplace,  606. 

Humphreys  and  Abbott  on  Mis- 
sissippi River,  372. 

Hunt,   T.  S.,  on  the  matter   of 


631 


space,  49,54;  on  moon's  atmos- 
phere, 57;  on  primeval  chemis- 
try, 274;  on  a  plastic  zone,  315; 
on  orogeny,  333;  on  rock  ab- 
sorption, 461. 

Button,  F.  W.,  on  Mallet's 
theory,  319. 

Huxley,  T.  H.,  on  age  of  the 
earth,  180. 

Huvgens  cited,  496;  on  nebulae, 
575. 

Hyginus  crater,  changes  near, 
393,  395. 

Hyperbolic  orbit,  how  caused, 
74. 

Hypothesis  ripening  to  doctrine, 
152. 


I 


Ice  caps  of  Mars,  416. 

Ice-covered  planets,  446;  satel- 
lites, 442. 

Ice  periods,  290. 

Igneous  theory  of  Leibnitz,  559 
seq. 

Implications  excluded  from  nebu- 
lar theory,  196-8. 

Inclinations  in  planetary  systems, 
129,  171,  172,  621 ;  of  Uranian 
and  Neptunian,  153;  how  ex- 
plained, 154  seq. ;  of  axis  in- 
creased by  lagging  tide,  243; 
sometimes  diminished,  244. 

Incrustation  on  moon,  397. 

Incrustive  phase,  542. 

Index  of  rock  absorption,  460. 

Infinitude  of  worlds,  585. 

Initial  temperature  of  earth,  307. 

Intelligence  on  other  worlds,  502, 
592. 

Internal  tides,  action  of,  398. 

Intervals  between  orbits,  173. 

Invariable  plane  of  solar  system, 
172. 

Iron,  magnetic,  in  meteoric  dust, 
10. 

Iron  floating  on  molten  iron,  218, 
219. 

Isothermal  lines  in  crust,  275; 
ascent  of,  276,  324. 


Janssen  on  matter  around  the 
sun,  64. 

Jones,  G.,  on  zodiacal  light,  23, 
25. 

Jovian  phase,  543.  See  "Jupi- 
ter." 

Julien,  C-F.,  on  effect  of  preces- 
sion, 288. 

Jupiter,  condition  of,  149;  satel- 
lites of,  150 ;  tidal  influence  of, 
248;  why  having  several  satel- 
lites, 262 ;  physical  relations  of, 
425;  compared  with  earth,  427; 
trade  winds  on,  428;  cosmic 
periods  of,  429 ;  physical  condi- 
tion of,  430,  441,  543;  atmos- 
phere of,  430-1 ;  luminosity  of, 
432;  tides  on,  433,  434-7;  tides 
on  satellites  of,  438;  densities 
of  satellites  of,  440;  habita- 
bility  of,  505 ;  in  Kant's  theory, 
581. 

K 

Kant  on  comets,  27,  576;  on  or- 
ders of  nebulae,  140,  575;  on 
retardative  action  of  tides,  249, 
473,  580;  on  restoration  of  the 
cosmos,  492,  586;  on  habita- 
bility,  496 ;  general  cosmogony 
of,  574. 

Keferstein  on  a  plastic  zone,  315 ; 
on  plications,  332. 

Kepler  crater,  radial  streaks  of, 
390,  404. 

Kepler,  third  law  of,  159 ;  cosmic 
theory  of,  553. 

Kilanea,  218. 

King,  C.,  on  downthrows,  304; 
on  elevation  and  subsidence, 
317;  onTriassic,  362. 

Kirkwood,  D.,  on  meteoric  dust, 
11;  on  spiral  nebulae,  99;  on 
discoid  ring,  112;  on  direction 
of  rotation,  127;  on  density  of 
solar  nebula,  163;  on  masses  of 
Mars  and  Asteroids,  176;  on 
comets  as  members  of  solar  sys- 
tem, 181. 


632 


Klein,  H.  J.,  on  crater  Hyginus 
N,  393-4;  on  lunar  craters. 
408. 

Konig,  C.,  cited,  485. 

Kretz,  on  ether,  479. 

Kreutz  on  comet  of  1882  I,  31. 

Krummel  on  altitudes  of  conti- 
nents, 454. 

Krusenstern  on  a  fire  ball.  5. 


Lacolitic  mountains,  294. 

Lagging  of  tide.  231 ;  retards  ro- 
tation, 232,  396;  causes  reces- 
sion of  tide-producer,  239; 
greater  in  nucleus,  239;  in- 
creases inclination  of  axis,  243 ; 
retards  moon's  rotation,  249, 
396  seq. ;  when  discordant,  398. 

Lake  survey  on  Niagara  gorge, 
3/1. 

Lambert,  J.  H.,  on  cosmogony, 
597. 

Lancetta  on  dust  falls,  11. 

Lane,  H.,  on  solar  heat,  83;  on 
central  density  of  sun,  162. 

Langley,  S.  P.,  on  absorbent  me- 
dia in  space,  61,  64,  381;  con- 
sequences of,  413. 

Laplace  on  zodiacal  light,  24;  on 
rotation  of  resulting  mass,  121, 
614;  on  comets  as  strangers  in 
our  system,  182,  610,  615;  on 
annulation,  187,  613;  on  tides, 
225;  on  change  of  axis,  334;  on 
tidal  retardation,  474;  on  sta- 
bility of  system,  478;  on  habi- 
tability,  496,  606;  on  the  sys- 
tem of  the  world,  606-17;  criti- 
cism of,  on  Newton,  607;  con- 
fidence of,  in  his  hypothesis, 
610;  on  lunar  synchronism, 
616. 

Lardner  on  habitability,  496. 

Larkin,  E.  L.,  on  forces  of  na- 
ture, 223. 

Lasell  on  Omega  nebula,  89. 

Laurentian  tides,  266. 

Lava  ejections  on  moon,  399,  403, 
408-9. 


Lava  floating,  218. 

Lava  floes  on  incrusting  planets, 
397. 

Lava  floods,  517:  on  moon,  399, 
403. 

Leibnitz  on  earth's  interior,  339, 
558-63;  on  atoms,  553;  on  cos- 
mogony, 558;  on  monads,  571. 

Leipoldt  on  heights  of  continents, 

Lenz  on  meteoric  dust,  9. 
Leonids,  21. 
Le  Sage  cited,  620. 
Lescarbault  on  Vulcan,  215. 
Lesley,    J.  P.,    on   downthrows, 

304. 

Leucippus  cited,  553. 
Levelling  of  land,  454. 
Leverrier  on  Tempel's  comet,  33. 
Lewis,  H.  C.,  on  geological  time, 

378. 

Liais  on  zodiacal  light,  24. 
Librations,  132. 

Lichtenberg,  Hofrath,  cited,  582. 
Lichtenstein  on  meteors,  16. 
Light,      wave    lengths     of,     37; 

evolved  in  collisions  of  cosmic 

atoms,    73;     of    comets,    how 

caused,  77. 

Limie  crater,  392,  395. 
Liquefaction  of  water,  270. 
Liquefaction     from     diminished 

pressure,  221. 
Liquid    matter     forming    on    a 

planet,  217. 
Liquid  nucleus,  340. 
Liveing  on  Lockyer's  theory,  49: 

on  Siemens'  theory.  57. 
Lockyer,  J.  N.,  on  compound  na- 
ture of  elements,   48,    56;   on 

heat  of  Orion  nebula,  532. 
Lodge,  0.,  on  ethereal  origin  of 

matter,    49;   on    water    under 

pressure,  270. 

Logan,  W.,  on  Eozoic,  359. 
Lohrman  on  moon,  385,  392. 
Loornis,  E.,  on  Martial  climate. 

417. 
Levering,  J.,  on  phosphorescence, 

5. 
Lucretius  cited,  553,  591. 


INDEX. 


633 


Luminosities  of  planets,  432. 

Lunar  phase,  544. 

Lunar    tide,   248;    in    primitive 

times,     258;    influence    of    in 

mountain   making,    326.      See 

"Tides." 
Lyell,  C.,  on  age  of  the  earth, 

'180 ;  on  crushing  of  strata,  322 ; 

on  time  ratios,  363;  on  Niagara 

gorge,  369. 

M 

Macvicar,  J.  G.,  on  constitution 
of  matter,  49. 

Maedler  on  firmamental  rotation, 
140;  on  crater  Linne,  392. 

Magellanic  clouds,  42;  changes 
in,  88. 

Mallet,  J.  W.,  on  solidifying  iron, 
218;  on  unequal  radial  shrink- 
age, 303;  on  mashing  of  strata, 
319;  on  orogeny,  334;  on  heat 
from  crushing,  346. 

Man's  position  among  intelli- 
gences, 592. 

Marcou,  J.,  on  Niagara  gorge, 
369. 

Marine  tides  in  early  times,  256. 

Mars,  satellite  of,  with  period  too 
short,  168 ;  axial  retardation  of, 
250 ;  why  having  two  satellites, 
262;  phenomena  of,  415;  age 
of,  415;  tidal  influences  on,  417: 
atmosphere  of,  419;  boiling 
water  on,  409 ;  habitability  of, 
503. 

Marsh,  Gr.  P.,  on  floating  lava, 
218. 

Martial  phase,  544. 

Martins,  C.,  on  astronomical  cli- 
mates, 290. 

Marx  on  meteoric  dust,  9. 

Mashing  together  in  orogeny,  302, 
319-23,  324. 

Matter,  finite  existence  of,  546, 
584. 

Matter,  of  space,  opinions  on,  49, 
200 ;  tabular  conspectus  of,  65 ; 
aggregation  of,  66 ;  as  a  resist- 
ing medium.  104,  169,  478-81. 


Maundeville,  Sir  John,  on  form 

of  earth,  552. 
Maupertuis  cited,  553,  575. 
Maximum  internal  temperature, 

221. 
Maxwell  on  plurality  of  worlds, 

497. 
Maxwell,  C.,  cited,  412,  493;  on 

Saturn's  rings,   121,   179,   582; 

on  terrestrial  cooling,  296. 
McGee,   J.  W.,   on  ice  periods, 

290. 
Mechanical    constitution  of    the 

world,  589;    not  atheistic,  591. 
Mercury,  tides  on,  250,  424,  476 ; 

why  'having  no  satellite,  262; 

planetography  of,   423;  condi- 
tions on,  424;  erosion  on,  457; 

habitability  of,  500. 
Meridional    trends,    252-4,    325; 

strictly  submericlional,  254;  in 

the  earth,   350;    primitive    in 

origin,  353. 

Messier  craters,  393,  395. 
Metamorphism  of  rocks,  276,  315; 

in  mountain  making,  331. 
Meteoric   dust.     See    "Cosmical 

dust." 

Meteoric  streak,  5;  stones,  15. 
Meteoroidal  resistance,  70,  480. 
Meteoroidal  swarms,  17  seq.,  75, 

482;  table  of,  21;  number  of, 

22. 
Meteors,  3,  trains  of,  5;  number 

of,  13,  22;  height  of,  15;  ve- 
locity of,  16:  Von  Reichenbach 

on,  75-6. 
Milky  Way,  T.  Wright  on,  572; 

Kant  on,  574,  583,  586;  central 

body  of,  589;  Lambert  on,  598; 

W.  'Herschel  on,  598;  Laplace 

on,  609. 
Mill,  J.  S.,  on  nebular  theory, 

153. 

Miller,  W.,  on  habitability,  497. 
Mitchel  on  Pleiades,  612. 
Mitchell,  Maria,  on  meteors,  5. 
Molecule,  permanence  of,  547. 
Molten  matter,  outflowing  tidal- 

ly,  265,  399;   sources   of,  344; 

zone  of,  344;   outflows  of    on 


634 


INDEX. 


earth,  401 ;  on  temporary  stars, 
517,  543. 

Molten  nucleus,  theory  of,  294, 
340. 

Molten  phase,  217,  542. 

Momentum,  angular,  of  rotation, 
109. 

Monads,  571. 

Mont  Blanc,  section  across,  308. 

Moon,  atmosphere  of,  absorbed, 
57,  382;  tides  on,  248;  retarda- 
tion of,  on  axis,  249;  disappear- 
ance of  water  on,  251;  origi- 
nating from  disruption  of 
earth,  259;  influence  of  in 
mountain  making,  326;  planet- 
ogenic  history  of,  379  seq. ; 
planetary  relations  of,  379;  age 
of,  380;  early  condition  of,  381 ; 
atmosphere  of  wanting,  381; 
physical  aspects  of,  385;  map 
of,  386;  craters  on,  386  seq. ; 
radial  streaks  on,  390;  furrows 
or  clefts  on,  391;  changes  on, 
392-5,  414 ;  tidal  evolution  of, 
395;  retarded  rotation  of,  396 
seq. ;  incrustation  of,  397 ;  ero- 
sion on,  457;  synchronism  of, 
404,  557,  580,  616;  habitability 
of,  502. 

Morande,  Rey  de,  on  colder  cli- 
mates, 487. 

Morris,  C.,  on  Siemens'  theory, 
57;  on  habitability,  498;  on 
matter  in  space,  61. 

Morrison  on  comet  of  1882  b,  31. 

Mountain  crests  thinned,  335. 

Mountain  making,  291-335;  sep- 
arate conceptions  on,  323-7; 
Leibnitz  on,  562;  aeriform 
agents  in,  292. 

Mountains  of  elevation,  291 ;  of 
relief,  291. 

Mountain  forms  in  cooling  iron, 
219. 

Mousson  on  freezing  under  pres- 
sure, 271. 

Murphy,  J.  J.,  on  effect  of  pre- 
cession, 288;  on  eccentricity, 
290. 

Murray  on  meteoric  dust,  11. 


N 

Xasmyth  on  moon,  385,  621. 

Nebulae,  35-48,  80-142;  physical 
condition  of,  40;  forms  of,  42, 
99,  117,  601,  604,  605;  spectra 
of,  42-8,  192,  531;  evolution 
of,  73,  105;  heat  of  from  re- 
frigerative  contraction,  81  ; 
heat  of  from  aggregation,  92- 
4;  changes  of  form  in,  87-94; 
rotation  of,  94-106;  approach 
of,  95 ;  spiral  forms  of,  99-102 ; 
sickle  forms  of,  102-3;  evolu- 
tion of  without  rotation,  105, 
118;  local  nuclei  in,  106,  118; 
annulation  of,  106-19;  non-an- 
nulating,  105,  118;  spheration 
of  ring  from,  119-42;  influ- 
enced by  cosmic  tides,  129; 
currents  on,  130;  orders  of,  139; 
distinction  of  firmamental  and 
solar,  146;  cosmogonic  condi- 
tions of.  531 ;  formation  of,  66, 
533;  Herschel  on,  599,  601-4; 
Laplace  on,  606. 

Nebular  stage,  540. 

Nebular  theory  verified  by  facts, 
147;  presumptions  sustaining, 
151;  indictments  against,  152, 
198 ;  supported  by  great  names, 
153;  objections  to,  153-95;  does 
not  assume  complete  continu- 
ity of  primitive  matter,  185; 
does  not  imply  an  absolute  be- 
ginning, 196;  nor  explain  ori- 
gins, 196;  nor  exclude  plan 
and  purpose,  197;  as  modified 
by  Faye,  198-212;  as  modified 
by  Spiller,  212-4. 

Neison  on  moon,  385;  on  crater 
Linne,  393;  on  Hyginus  N., 
394. 

Nelson  on  comet  of  1882  b,  31. 

Neptune,  apsides  of,  285;  habit- 
ability  of,  499,  506. 

Neptunian  system  retrograde,  1 53, 

dewberry,   J.    S.,   on    primitive 

tides,  265. 
Sewcomb,  S.,  on  dense  clusters 


INDEX. 


635 


of  stars,  48 ;  on  solar  heat,  83 ; 
on  discoid  ring,  112 ;  on  inter- 
vals between  orbits,  173;  on 
age  of  the  sun,  179,  356;  on 
terrestrial  rigidity,  341;  on 
solar  spots,  520;  cited,  425,  601. 

Newton,  H.  A.,  on  meteors,  7. 

Newton,  Sir  I.,  on  an  interplan- 
etary medium,  50,  479;  on 
planetary  orbits,  172;  on  tides, 
225;  on  divine  agency,  607; 
cited,  339. 

Niagara,  gorge  of,  369,  378,  4-52. 

Niesten  on  comets,  27. 

Nilotic  delta.  372. 

Nordenskjold  on  meteoric  dust, 
8. 

Norton,  W.  A.,  on  comets,  78. 

November  meteoric  shower,  14, 
17  seq.,  33. 

Nucleated  phase,  541. 

Nucleating  phase,  540. 

Nucleus  of  planet  in  liquid  stage, 
217;  becoming  solid.  220,  323. 

Nucleus  of  stars.  526. 

Nutations,  132,  616. 


Objections  often  trivial,  194; 
from  planetary  motions,  153- 
70:  from  planetary  positions, 
171-5;  from  planetary  masses 
and  densities,  175-9;  from  ter- 
restrial duration,  179-81 ;  from 
comets,  stars  and  nebula?,  181- 
6;  of  an  anonymous  writer, 
194. 

Oblateness  varying  with  rotation, 
278. 

Obliquity  of  axis,  effects  of,  282-5. 
See  "Inclinations." 

Ocean,  birth  of,  273 ;  influence  of 
in  mountain  making,  301,  325, 
329,  331 ;  basin  of,  how  formed, 
335;  volume  of,  466;  depth  of, 
466;  bottom  configuration  of, 
302. 

Oceanic  trends,  352. 

Gibers'  crater.  390. 

Olbers  on  origin  of  asteroids,  177. 


Old  age  of  planets,  451. 

Olmstead.  D..  on  meteors,  16;  on 
zodiacal  light,  23,  26. 

Omega  nebula,  changes  in,  88, 
89,  90. 

Oppplzer  on  origin  of  meteors,  33. 

Orbital  motion,  retardation  of, 
281. 

Orbital  movements,  of  three 
bodies  in  space,  66,  95 ;  when 
attraction  varies  with  the  dis- 
tance, 202. 

Orbits,  of  meteoric  swarms,  17 
seq. ;  of  comets,  how  determin- 
ed, 73-4;  of  satellites,  how  in- 
verted, 155;  how  inclined,  171. 

Orbits  assumed  described  in  prim- 
itive nebula,  201. 

Orders  of  nebula?,  139. 

Orion,  nebula  in,  42,  45;  changes 
of  form  of,  88,  611 ;  curdling 
Huygenian  region  in,  105; 
spectrum  of,  531;  stars  in, 
525. 

Orogenic  forces,  291-335,  326. 

Orogenic  history,  final  conception 
of,  326-35,  334;  conspectus  of 
views  on,  332. 

Oscillation  on  an  axis,  132;  of 
earth,  260;  of  levels.  280. 

Overturn  of  a  system,  154-5. 


Palaeozoic  tides,  263. 

Parabolic  orbit,  how  caused,  74. 

Parsons,  S.,  on  meteoric  resist- 
ances in  space,  70 ;  on  periodic 
times,  167;  on  rotary  motion, 
170;  on  age  of  the  earth,  179, 
180 ;  on  comets  as  an  objection, 
181;  on  tenuity  of  primitive 
nebula,  184;  on  improbability 
of  annulation,  186;  against 
nebular  theory,  198. 

Peirce,  B.,  on  rings  of  Saturn,  35, 
582;  on  solar  heat,  81;  on  in- 
tra- Jovian  ring,  177. 

Periodic  times  alleged  too  long, 
158;  alleged  too  short,  167. 

Periods,  geological,  365. 


636 


INDEX. 


Perrey,  A.,  on  earthquakes,  348. 

Perseids,  21. 

Pfaff,  F.  on  mountain  making, 
312. 

Phases  of  star  life,  529,  541 ;  of 
planet  life,  543. 

Phobos,  periodic  time  of  too  short, 
168;  tidal  action  of,  418;  fall- 
ing to  Mars,  481. 

Photospheric  matter,  527  seq., 
541  seq. 

Pickering,  E.  C.,  on  variable 
stars. 

Pilar,  G.,  on  the  ice  age,  290. 

Plan  not  excluded,  197. 

Planetary  nebulae,  46. 

Planetogenic  constants,  table  of, 
449 ;  remarks  on,  450. 

Planetogeny  of  Leibnitz,  564;  of 
Kant,  577. 

Planets  of  other  systems,  512. 

Plastic  zone,  313,  315,  323,  325. 

Plicated  strata  beneath  impli- 
cated, 301. 

Plications,  801,  304;  not  always 
accompanying  elevation,  304; 
localization  of,  305 ;  amount  of. 
318.  See  "Wrinkles." 

Pliny  cited,  552. 

Plummeron  nebular  spectra,  192. 

Plutarch  cited,  385. 

Plutonic  theory,  563. 

Poisson  on  meteors,  16;  on  tem- 
perature of  space,  199,  208. 

Polar  lands  affected  by  rotation, 
280. 

Polar  snows  affected  by  inclina- 
tion of  axis,  284;  by  precession, 
287;  by  changes  in  eccentricity, 
289. 

Powell,  J.  W.,  on  downthrows. 
304. 

Pratt,  Archdeacon,  on  unequal 
radial  shrinkage,  303;  on  dens- 
ity under  mountains,  330;  on 
terrestrial  rigidity,  341,  342; 
on  central  density,  345. 

Precession,  effects  of,  285,  290. 

Precipitation,  of  planets,  478, 
621;  on  temporary  star,  516, 
518;  Kant's  doctrine  of,  586. 


Prel,  du,  on  habitability,  497. 

Prenebular  stage,  539. 

Pressure  causing  central  solidifi- 
cation, 220. 

Pressure,  lateral,  in  orogeny. 
See  "Wrinkling,"  "Plica- 
tions," etc. 

Preston,  S.T.,on  Lodge's  views, 49. 

Prevost,  C  ,  on  a  wrinkling  crust, 
296. 

Primitive  earth,  558-63. 

Primitive  wrinkles  meridional, 
254;  tidal  phenomena,  264. 

Proctor,  R.  A.,  on  zodiacal  light, 
24;  on  nebular  theory,  194;  on 
lunar  changes,  394;  on  Jupiter, 
431;  on  ultra-Jovian  pliinets. 
443;  on  habitability,  497. 

Projectile  force  on  moon,  400. 

Prolateness,  tidal,  130,  226;  of 
moon,  407. 

Protogsea  of  Leibnitz,  558. 

Purgatory  action  of  tide,  400. 

Purpose  not  excluded,  197. 

Pyrolithic  crust,  365,  366. 


Quantitative   relations   of    tides, 

228. 

Quaternary  period,  cold  of,  289. 
Queengouck.  meteoric  fall  at.  11, 

12. 


Races,  antiquity  of,  379. 

Radial  shrinkage,  303. 

Radial  streaks  on  moon,  391 ; 
cause  of,  403. 

Radius  of  gyration,  162-3,  437. 

Radius  vector,  107,  124. 

Rafinesque  cited,  572. 

Rains,  first  descent  of,  273,  327 ; 
on  moon,  401. 

Ramsay,  And.,  on  time  ratios, 
364. 

Ranges  of  mountains,  305:  im- 
possible on  contractional 
theory,  308. 

Rankine  on  reconcentration  of 
energy,  492. 


INDEX. 


637 


Rate  of  downward  increase  of 
heat,  376. 

Rate  of  planetary  cooling,  216. 

Rayet  and  Wolfe  quoted,  514. 

Reade,  T.  M.,  on  age  of  the  earth, 
180;  on  continental  erosion, 
373,  374. 

Recession  of  planets,  160;  of  tide- 
producer,  239:  of  moon  traced 
backward,  259,  326 ;  of  Niagara 
falls,  369  seq. ;  of  St.  Anthony 
falls,  372;  of  lake  bluffs,  374, 
378. 

Reclus,  E.,  cited,  373. 

Reconcentration  of  energy  in  our 
system,  207. 

Red  spot  on  Jupiter,  429. 

Refrigeration,  final,  484;  deduc- 
tive views  on,  487. 

Reichenbach  on  meteoric  dust,  8, 
76;  on  meteors,  75-6. 

Relief  of  internal  pressure,  345. 

Resisting  medium  in  space,  in- 
fluence of  on  nebulae,  104;  on 
satellites,  169 ;  on  planets,  477. 
See  "'Matter  in  space." 

Respighi  on  zodiacal  light,  24. 

Retardation  of  orbital  motion, 
281. 

Retardation,  of  rotary  motion 
from  lagging  tide,  232-9,  404; 
on  the  moon,  248,  396  seq.,  404; 
from  surface  fluids,  250;  of 
earth's  rotation  traced  back- 
ward, 250 ;  effects  of,  278,  473-5 ; 
how  produced,  405;  on  Jupiter, 
435-7 ;  on  ultra-Jovian  planets, 
447;  amount  of,  474. 

Retral  movement  of  tide,  234; 
causes  meridional  structure, 
253,  254 

Retrograde  rotation,  how  result- 
ing, 123  seq.,  135,  157;  alleged 
necessary  in  primitive  stage, 
127;  tendency  from  centrifugal 
force,  133;  case  of  in  Uranian 
system,  153-8 ;  may  result  from 
collisions,  120,  157;  or  from 
formative  conditions  (Faye), 
158. 

Reversal  of  spectroscopic  lines, 40. 


Revivification  of  a  cosmos,  491, 
621;  Spencer  on,  492;  Rankine 
on,  492;  Kant  on,  492,  586; 
Clausius  on,  493. 

Riccioli  on  crater  Linne,  392. 

Richthofen  cited,  354. 

Ricketts,  C.,  on  subsidence  of 
crust,  316. 

Rigidity  of  earth  maintained,  340, 
342;  "tested  by  tides,  342-3. 

Ring,  abandonment  of,  110,  613; 
width  of,  111;  discoid  form  of, 
alleged,  111-2;  involving  entire 
nebula,  117;  stratification  of, 
119,  176,  582;  rupture  and 
spheration  of,  119-42,  614;  in- 
stability of,  121;  alleged  im- 
probable, 186;  conception  of, 
in  cosmogony,  620. 

Rivers,  trends  of,  353. 

Roche,  on  zodiacal  light,  25;  on 
Saturnian  rings,  168;  on  the 
origin  of  the  solar  system,  214. 

Rocks,  thickness  of,  359  seq. ;  ab- 
sorption by,  461  seq. 

Roots  of  mountains,  321. 

Roscoe  on  spectral  analysis,  40. 

Rosmini  cited,  553. 

Rosse,  Lord,  telescope  of,  36;  on 
lunar  temperatures,  381,  414. 

Rotation  of  nebulas,  94-106;  with- 
out impact,  98,  118;  of  mass 
resulting  from  spheration,  121 ; 
influenced  by  cosmic  tides,  129 ; 
influenced  by  external  attrac- 
tions, 131 ;  summary  of  princi- 
ples on,  134;  alleged  without 
adequate  cause,  170. 

Rotation  of  planets,  effect  of 
changes  in,  278 ;  tidally  retard- 
ed, 232-9. 

Rotation  of  earth  in  primitive 
times,  259. 

Rutherford  on  composition  of 
stars,  191. 


Saemann,  L.,  cited,  621;  on  ab- 
sorption of  fluids,  382,  465,  468 ; 
on  depth  of  ocean,  466;  error 
of,  466.  468. 


638 


INDEX. 


Saigey  on  the  constitution  of 
matter,  66. 

Satellites,  tides  on,  248,  438;  con- 
ditions of  detachment  of,  262; 
Jovian  tides  caused  by,  435; 
tides  on,  438,  458;  varying  light 
of,  440;  Jovian,  water-covered, 
441;  'synchronous  motions  of, 
477,  616. 

Saturn,  why  having  several  satel- 
lites, 262 ;  physical  condition  of, 
442,  443-8;  an  ice-covered 
planet,  446;  in  Kant's  theory, 
576,  579. 

Saturn  ian  rings,  35,  482 ;  rotation 
of,  168;  not  continuous,  185; 
disintegration  of,  483 :  Kant  on, 
581. 

Schellen  on  spectral  analysis,  39 ; 
on  nebulap,  44,  88,  117." 

Schiaparelli  on  meteoric  orbits, 
17;  on  comet  of  1882  b,  31;  on 
cometary  origin  of  meteors,  33. 

Schmeizer  cited,  330. 

Schmidt,  J.  F.  J.,  on  meteoroids, 
21 ;  on  comet  of  1882  b,  31 ;  on 
map  of  moon,  385;  on  crater 
Linne,  392. 

Schroter  on  Venus,  423;  on  Mer- 
cury, 425. 

Schuster  on  meteoric  dust,  11 ;  on 
Lockyer's  views  concerning 
matter,  49. 

Scintillations  of  stars,  69. 

Scrope,  Poulett,  on  volcanic  moun- 
tains, 330. 

Secchi  on  zodiacal  light,  24;  on 
nebulap,  45;  on  crater  Linne, 
392;  on  Martial  atmosphere, 
417;  on  Jovian  satellites,  440; 
on  double  stars,  513;  on  solar 
spots,  520;  on  types  of  stars, 
522,  529. 

Secondaries,  rotations  of,  125. 

Sedgwick  on  a  wrinkling  crust, 
295. 

Sedimentation  along  geosyncli- 
nals,  314-9,  324,  327 ;  insuffi- 
ciency of  theory  of,  317. 

Sediments,  a  measure  of  time, 
356,  451 ;  from  rivers,  453. 


Seistnism  from  tidal  action,  325, 
348. 

Selenography,  385  seq. 

Seleucus  cited,  551. 

Shrinkage,  from  cooling,  302;  ra- 
dial, 303 ;  as  cause  of  accelera- 
tions, 359.  See  ''Wrinkling." 

Sickle-shaped  nebulae,  43,  causes 
of,  102. 

Siemens,  W.,  on  matter  in  space, 
57;  on  perpetuation  of  sun's 
heat,  57;  criticisms  on,  61;  in 
reply  to  criticisms,  62,  63 ;  fur- 
ther references  on,  65. 

Silicates  floating,  219. 

Simmons,  G.  W.,  on  comet  of 
1881,  29. 

Sirian  phase,  541. 

Sirius  the  centre  of  Milky  Way, 
589. 

Skinner,  A.  N.,  on  comets,  29. 

Slaughter,  W.  B.,  on  nebular  ro- 
tation, 94;  on  angular  velocity. 
109:  against  nebular  theory, 
153;  basing  objection  on  peri- 
odic times,  158;  on  angular 
velocities,  159;  on  rotary 
motion,  170;  on  inclinations 
of  orbits,  171 ;  on  densities 
of  outer  planets,  177. 

Slipping  of  crust,  308-10. 

Snow  on  Mars,  416. 

Solar  phase,  542. 

Solar  System,  origin  of,  145. 

Solar  tides  contributing  to  separa- 
tion of  moon,  260.  See  "Sun." 

Solidification,  at  surface,  218;  at 
centre,  220;  at  centre,  not  a 
normal  freezing,  271,  346;  un- 
der pressure,  270 ;  rationale  of, 
271. 

Solidity,  a  relative  property,  223 ; 
of  a  planet  supposed  necessary, 
220. 

Soret's  formula,  412. 

Spectra,  classes  of,  38;  of  comets, 
27;  of  nebula?,  42-8,  192,  531; 
of  fixed  stars,  191,  522  seq., 
532;  significance  of  nebular. 
192,  532. 

Spectroscope  explained,  37. 


INDEX. 


639 


Spencer,  H.,  on  spiral  nebulae, 
102 ;  on  origin  of  asteroids,  177 ; 
on  comets,  181 ;  on  implications 
of  nebular  cosmogony,  197;  on 
equilibration,  488;  on  restora- 
tion of  cosmos,  492,  494. 

Sphe ration  of  nebular  rings,  119- 
42,  614,  620. 

Spiller  on  nebular  theory,  212-4. 

Spiral  nebulae,  42,  44;  causes  of, 
99-102,  104. 

Spiro-annular  nebulae,  44. 

Spots  on  sun,  520,  556. 

Sprengel  air  pump,  201. 

Stage  of  development,  of  planet, 
216;  of  Jupiter,  429,  430,  431; 
on  ultra-Jovian  planets,  446. 

Stages  of  world  life,  438-44. 

St.  Anthony  gorge,  372,  378. 

Stars,  multiple,  511;  temporary, 
513-18;  variable,  518;  grada- 
tions of,  522;  distribution  of 
substances  among,  525;  heat 
of,  526;  two  stages  in  life  of, 
526 ;  darkened  560. 

Steam,  in  mountain  making,  292, 
325 ;  limit  to  elasticity  of,  293-4. 

Steel,  specific  gravity  of,  218; 
flotation  of,  218. 

Stellar  nebulae,  47. 

Stellar  stage,  541. 

Stellation,  incipient,  53. 

Steno  cited,  563. 

Stevenson,  J.  J.,  on  desiccation, 
471. 

Stockwell,  J.  N.,  on  orbital  incli- 
nations, 173;  on  eccentricity, 
368. 

Stone,  E.  J.,  on  tidal  retardation, 
474. 

Storm  secular,  on  earth,  272,  327; 
on  moon,  401 ;  on  Jupiter,  433 ; 
on  sun,  490. 

Strabo  on  upheavals,  292. 

Strata,  thicknesses  of,  350  sea. ; 
table  of,  363. 

Stratification  of  a  ring,  119,  176, 
582. 

Struve,  Otto,  on  nebulae,  42,  88; 
on  Saturn's  rings,  483;  on 
double  stars,  512. 


Struve,  W.,  on  double  stars,  512. 

Studer  cited,  339. 

Submeridional  trends.  See  "  Me- 
ridional." 

Subsidence  of  ocean's  bottom,  277, 
314-9;  under  load  of  sediments, 
314-9;  on  removal  of  load, 
317. 

Suess  on  mountain  making,  294. 

Sulphur  showers,  7. 

Sun,  central  density  of,  162;  ro- 
tary velocity  of,  166;  density 
of,  less  than  formerly,  190; 
tides  caused  by,  247,  250,  475; 
refrigeration  of,  484-7,  489;  as 
a  variable  star,  519;  Kant's 
doctrine  of,  587. 

Superficial  solidification,  218. 

Swarms  of  meteoroids,  17  seq. ; 
gathering  of,  72. 

Swedenborg,  E.,  on  cosmology, 
566. 

Swift,  L.,  on  intra-Mercurial 
planets,  216. 

Sylvestri  on  a  dust  fall,  11. 

Synchronistic  motions,  130-4;  ul- 
timate, 134,  248,  473-7;  on 
Mercury,  250;  on  the  earth, 
251;  primitive,  of  earth  and 
moon,  259;  of  moon,  396  seq., 
404,  557,  580,  615;  of  Jovian 
satellites,  439. 

Synchronistic  phase,  544. 

Synclinal  structure  in  mountains, 
314-9. 

Synclinorium,  defined,  322;  com- 
pleted, 328. 


Tacchini  on  atmospheric  dust,  11. 

Tails  of  comets,  77,  78. 

Tangential  pressure  in  orogeny. 
See  "  Wrinkling,"  "  Plica- 
tions," etc. 

Tebbutt  on  comet  of  1881,  29. 

Temperature,  lowering  of,  485; 
of  earth's  interior,  307. 

Temporary  stars,  513-8,  543,  609. 

Tenuity  of  primitive  nebula, 
alleged  too  great,  184;  calcu- 
lations on,  200. 


640 


INDEX. 


Terrace  formation,  rate  of,  374. 

Terrestrial  phase,  543. 

Theophilus  crater,  338. 

Thickness  of  mountain  strata, 
317. 

Thicknesses  of  formations,  363. 

Thomson,  J.,  on  freezing  point, 
270. 

Thomson,  Sir  William,  on  heat 
of  meteors,  16;  on  meteoric 
orbits,  17;  on  the  ether,  52,  54, 
55;  on  solar  heat,  81;  on  age 
of  the  world,  179,  356,  364;  on 
solidifying  minerals,  218;  on 
increase  of  temperature  down- 
ward, 221;  on  terrestrial  ob- 
lateness,  267;  on  freezing  point 
under  pressure,  270,  272;  on 
unequal  rate  of  rotation,  279; 
on  geological  climates,  290 ;  on 
a  problem  in  therm  ics,  305;  on 
change  of  axis,  334;  on  inter- 
nal liquidity,  340,  342;  on 
liquidity  from  crushing,  347; 
on  measurement  of  tides,  350; 
on  effect  of  ice  covering,  376; 
on  tidal  retardation,  473;  on 
constitution  of  comets,  482;  on 
colder  climates,  486,  487;  on 
dissipation  of  energy,  489 ;  on 
vortex  atoms,  569. 

Thomson,  Sir  Wyville,  on  ocean 
bottom,  302 ;  on  depth  of  ocean, 
466. 

Thought  in  the  cosmos,  197; 
unity  of,  508. 

Tidal  action  in  planetary  history, 
222-69;  three  general  cases  of, 
225;  general  effects  of,  230;  re- 
ciprocity of,  245-6;  detaching 
moon,  260;  erosion  by,  268;  in 
mountain  making,  325. 

Tidal  evolution  of  moon,  395  seq. 

Tides,  cosmic  in  a  nebular  sphe- 
roid, 129;  crushing  influence 
of,  131;  synchronistic  tendency 
of,  134,  248;  action  of,  accorcl- 
ing  to  Spiller,  213;  action  of, 
in  planetary  history,  222-69; 
some  elementary  principles  of, 
222;  theories  of,  225;  oceanic 


conditions  of,  225;  deforma- 
tive,  226;  compound,  226;  film. 
227;  quantitative  relations  of, 
228;  resulting  from  centrifu- 
gal action,  229;  lagging  of, 
231;  sliding  retrally,  233,  253; 
translatory  motion  of,  234,  351 ; 
anticipation  of,  234;  this  great- 
est along  equator,  235 ;  discord- 
ant, 239;  causing  recession  of 
tide  producer,  239 ;  on  tide  pro- 
ducer, 246;  caused  by  sun,  247; 
causing  synchronous  motions, 
248;  geal,  on  the  moon,  248, 
249;  on  satellites,  248;  meridi- 
onal structure  caused  by,  252- 
4;  producing  outflows  of  mol- 
ten matter,  255;  crushing  in- 
fluence of,  255;  marine,  in 
early  history,  256;  erosion  by, 
268 ;  influence  of,  in  mountain 
making,  320:  beneath  the 
crust,  336;  used  to  test  earth's 
rigidity,  342,  343;  connected 
with  earthquakes,  348;  action 
of,  on  moon,  383  seq.;  geal, 
height  of,  on  moon,  384;  action 
of,  after  incrustation,  398,  404 ; 
amount  of,  on  Mars,  417 ;  gen- 
eral formula  for,  418;  influ- 
ence of,  on  Venus,  420;  influ- 
ence of  on  Mercury,  424;  on 
Jupiter,  433,  434-6;  on  Jovian 
satellites,  438;  on  ultra-Jovian 
planets,  447;  retardation  by, 
on  earth,  474;  solar,  on  earth, 
475. 

Time,  geological,  355  seq. ;  diffi- 
culties of  numerical  calcula- 
tions of,  377 ;  summary  of  re- 
sults on,  377-8. 

Time  ratios,  356;  table  of,  365. 

Tissandier,  G.,  on  atmospheric 
dust,  6,  9,  11. 

Todd,  J.  E.,  on  changes  in  rota- 
tion, 279. 

Tra.lrs  and  anti-trades,  260. 

Trade  winds  on  Jupiter,  428. 

Trends,  meridional,  252,  253;  in 
the  earth's  structure,  350. 

Trifkl  nebula,  91. 


INDEX. 


641 


Trouvelot,  L.,  drawings  by,  42, 
90,  91. 

Trowbridge,  D.,  on  nebular  an- 
nulation,  113;  on  periodic 
times,  158;  on  density  of  solar 
nebula,  161-3;  on  rotary  velo- 
city, 165;  on  the  asteroidal 
ring,  177. 

Twisden,  I.  F.,  on  change  of 
axis,  334. 

Tvcho  crater,  389;  radial  streaks 
'of,  390,  404. 

Types  of  stars,  522. 

U 

Ueberweg  cited,  553. 

Ultra-Jovian  planets,  442;  ad- 
vanced stage  of,  444-8 ;  cosmic 
periods  on,  445;  ice-covered. 
446. 

Ultramundane  corpuscles.  620. 

Unity  of  the  world,  592. 

Universe,  evolution  of.  not  im- 
plied. 196. 

Upheaved  bv  aeriform  agents. 
292. 

Upheaval  of  synclinorium,  318. 

Uranian  system,  153  (teg..  157. 


Vapor,  first  condensation  of,  272. 

Vapors  beneath  crust,  292.  323, 
325. 

Variable  phase.  542. 

Variable  stars,  518. 

Velocities  of  zones  of  a  nebular 
ring,  123. 

Velocity,  angular,  109;  increases 
with  contraction,  159 ;  changes 
in.  affecting  planetary  condi- 
tions, 278. 

Velocity,  linear,  109;  in  parts  of 
ring, "123;  increases  with  con- 
traction, 159 ;  passage  of,  from 
developmental  to  Keplerian, 
160, 166 ;  of  hydrogen  molecules, 
184. 

Vents,  volcanic.     See  ''Craters." 

Venus,  inclination  of  axis  of,  129 ; 
tides  on,  250;  why  having  no 


satellite,  262;  apsides  of,  422; 

erosion  on,   457;    habitability 

of,  500. 
Verifications  of  nebular  theory, 

147. 
Viscosity  affecting  tides,  225,  231, 

241,  244,  246. 

Vogel  on  Lockyer's  views,  49. 
Volcanic  ranges,  331. 
Volcanic  vents  along  mountain 

axes,  335. 

Vortical  conception  in   cosmog- 
ony, 619. 
Vortices  of  Descartes,  555-6;  of 

Leibnitz,  564;  of  Swedenborg, 

566. 

Vulcan  (planet),  215. 
Vulcanism  from  tidal  action,  325. 

w 

Wabble  in  earth's  axis,  366-7. 
Wallace,    A.    R.,    on    geological 

climates.  290. 
Waltershausen  on  law  of  density, 

345. 
Warring,    C.    E.,    on    forces    of 

nature,  223. 
Water,  first  condensation  of.  272. 

327;  on  moon.  401. 
Watson,  J.  €.,  on  intra-Mercurial 

planets.  215. 

Wave  lengths  of  light,  37. 
Wave  theory  of  tides,  225. 
Weakness,  lines  of,  in  wrinkling, 

299. 
Whewell,  W.,  cited,  551,  566;  on 

plurality  of  worlds,  497. 
Whirlpool  motion  in  a  nebula, 

209. 

Whiston,  W.,  on  the  flood,  583. 
White,  C.  A.,  on  Laramie,  364. 
White,  I.  C.,  cited,  361. 
White  stars,  522. 
Whitney,  J.  D.,    on    mountain 

making,     294,    317,    332;    on 

thickening  of  formations,  317; 

on  desiccation  of    continents, 

471 ;  on  changed  climates,  485 ; 

on  lava  floods,  517. 
Width  of  nebular  ring.  111-7. 
Wilkes  on  zodiacal  light,  26. 


642 


INDEX. 


Williams.  A,  S.,  on  lunar  changes, 
394. 

Williams,  H.  S.,  on  distribution 
of  faunas,  281. 

Williams,  W.  M.,  on  the  matter 
of  space,  55;  on  solar  heat,  55; 
on  floating  iron,  219 ;  on  cool- 
ing cinder,  409;  on  Mercury, 
423. 

Wilson  on  comet  of  1882  b,  30. 

Winchell,  A.,  cited,  609;  on  dis- 
sociation, 471 ;  on  final  refriger- 
ation, 488;  on  cosmical  even- 
tualities, 490;  on  stages  of 
world  life,  538. 

Winchell,  N.  H.,  on  St.  Anthony's 
Falls,  372. 

Winlock  on  comet  of  1882  b,  31 

Winnecke's  comet  resisted,  429. 

World  stuff,  48-65. 

Worthen,  A.  H.,  on  distrbution 
of  faunas,  281. 

Wright.  A.  W..  on  zodiacal  light, 
24. 

Wright,  G.  F.,  on  geological 
time,  378. 

Wright  Thomas,  on  cosmogony, 
572,  589. 


Wright,  T.  F.,  on   Swedenborg, 

566,  571. 
Wrinkles,  primitive,  meridional, 

254;  in  bottom  of  ocean,  301; 

later  sometimes  transmeridion- 

al,  326. 
Wrinkling  crust,  theory  of,  294- 

314,  324;  illustration'of.  297-8, 

299,  300;  difficulties  of  theory 

of,  298-9. 
Wurtz  on  mashing  of  rocks,  320. 


Young,  C.  A.,  on  heat  of  nebulae, 
81 ;  on  periodic  time  of  Phobos, 
168;  on  solar  spots,  520. 

Young,  Dr.  T.,  on  the  ether,  53- 


Zodiacal  light,  23,  482,  484;  polar, 
iscopic  indications  of,  23 ;  Kant 
on,  583 ;  Laplace  on,  615. 

Zollner  on  luminosities,  432;  on 
variable  stars,  519,  521. 

Zone  of  molten  matter,  220,  344. 

Zones  of  climate  affected  by  obli- 
quity of  axis,  283. 


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